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The corefx repo contains the library implementation (called "CoreFX") for .NET Core. It includes System.Collections, System.IO, System.Xml and many other components. It builds and runs on Windows. You can 'watch' the repo to see Linux and Mac support being added over the next few months.
.NET Core is a modular implementation of .NET that can be used as the base stack for a wide variety of scenarios, today scaling from console utilities to web apps in the cloud. You can learn more about .NET Core and how and where you can use it in the .NET Core is open source and Introducing .NET Core blog posts.
The .NET Core Runtime repo contains the runtime implementation (called "CoreCLR") for .NET Core. It includes RyuJIT, the .NET GC, native interop and many other components.
Runtime-specific library code - namely mscorlib - lives in the CoreCLR repo. It needs to be built and versioned in tandem with the runtime. The rest of CoreFX is agnostic of runtime-implementation and can be run on any compatible .NET runtime. These characteristics were the primary motivation for the 2-repo structure.
Some of the best ways to contribute are to try things out, file bugs, and join in design conversations.
Want to get more familiar with what's going on in the code?
- Pull requests: Open/Closed
, 
and 
changes
Looking for something to work on? The list of up-for-grabs issues is a great place to start or for larger items see the list of feature approved. See some of our guides for more details:
You are also encouraged to start a discussion by filing an issue or creating a gist.
You can discuss .NET OSS more generally in the .NET Foundation forums.
Want to chat with other members of the CoreFX community?
The repo contains the following components. More libraries are coming soon. 'Watch' the repo to be notified.
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System.Collections. Provides classes that define generic collections, which allow developers to create strongly-typed collections.
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System.Collections.Concurrent. Provides a set of thread-safe collection types, instances of which may be used concurrently from multiple threads.
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System.Collections.Immutable. Provides a set of immutable collection types that make it easy to keep mutable state under control without sacrificing performance or memory footprint. You can read more about them on MSDN.
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System.Collections.NonGeneric. Provides classes that define various collections of objects, such as ArrayList, Hashtable, SortedList, Stack, and Queue. These collections exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
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System.Collections.Specialized. Provides classes that define specialized collections of objects, for example, a linked list dictionary, a bit vector, and collections that contain only strings. These collections exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
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System.ComponentModel. Provides interfaces for the editing and change tracking of objects used as data sources.
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System.ComponentModel.Annotations. Provides attributes that are used to define metadata for objects used as data sources.
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System.ComponentModel.EventBasedAsync. Provides support classes and delegates for the event-based asynchronous pattern. This pattern and these supporting types exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
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System.ComponentModel.Primitives. Provides interfaces that are used to implement the run-time and design-time behavior of components.
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System.ComponentModel.TypeConverter. Provides the System.ComponentModel.TypeConverter class, which represents a unified way of converting types of values to other types.
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System.Console. Provides the Console class, which enables access to the standard input, output, and error streams for console-based applications.
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System.Diagnostics.Contracts. Provides types and methods for representing program contracts such as preconditions, postconditions, and invariants.
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System.Diagnostics.Debug. Provides a class to interact with the debugger as well as methods for performing runtime assertions.
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System.Diagnostics.FileVersionInfo. Provides useful functionality for querying and examining the version information of physical files on disk.
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System.Diagnostics.Process. Provides access to local and remote processes, and enables the starting and stopping of local system processes.
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System.Diagnostics.TextWriterTraceListener. Provides trace listeners for directing tracing output to a text writer, such as System.IO.StreamWriter.
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System.Diagnostics.Tools. Provides attributes, such as GeneratedCodeAttribute, that are emitted or consumed by analysis tools.
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System.Diagnostics.TraceSource. Provides classes that help you trace the execution of your code.
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System.Dynamic.Runtime. Provides classes and interfaces that support the Dynamic Language Runtime (DLR).
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System.Globalization.Extensions. Provides classes for performing unicode string normalization, culture-specific string comparisons and support the use of non-ASCII characters for Internet domain names.
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System.IO. Provides base input and output (I/O) types that enable reading and writing data streams
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System.IO.Compression. Provides classes that support the compression and decompression of streams.
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System.IO.Compression.ZipFile. Provides static methods for creating and using Zip files.
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System.IO.FileSystem. Provides access to the file system, including support for enumerating and manipulating file system objects and for reading and writing files via streams.
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System.IO.FileSystem.DriveInfo. Provides the System.IO.DriveInfo class, which enables developers to query local drive information.
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System.IO.FileSystem.Primitives. Provides common enumerations and exceptions for path-based I/O libraries.
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System.IO.FileSystem.Watcher. Provides the System.IO.Watcher class, which listens to the system directory change notifications and raises events when a directory or file within a directory changes.
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System.IO.MemoryMappedFiles. Provides access to memory-mapped files, enabling code to read and write files by reading and writing memory.
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System.IO.Pipes. Provides types that enable a means for interprocess communication through anonymous and/or named pipes.
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System.IO.UnmanagedMemoryStream. Provides a stream for accessing unmanaged memory as represented by a pointer, as well as an accessor for reading and writing primitive types from unmanaged memory.
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System.Linq. Provides the foundation of Language-Integrated Query (LINQ), including LINQ standard query operators that operate on objects that implement
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System.Linq.Expressions. Provides classes, interfaces, and enumerations that enable language-level code expressions to be represented as objects in the form of expression trees.
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System.Linq.Parallel. Provides a parallelized implementation of LINQ to Objects. "Parallel LINQ" (PLINQ) implements the full set of LINQ standard query operators as well as additional operators specific to parallel operations.
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System.Linq.Queryable. Provides LINQ standard query operators that operate on objects that implement
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System.Net.Http. Provides a programming interface for modern HTTP applications. This includes HTTP client components that allow applications to consume modern web services over HTTP and HTTP components that can be used by both clients and servers for parsing HTTP headers, for example. This provides a consistent programming model on both the client and the server side for modern web services over HTTP.
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System.Numerics.Vectors. Provides a set of basic vector types that leverage single instruction, multiple data (SIMD) CPU instructions. See our recent announcements for more details.
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System.ObjectModel. Provides types and interfaces that enable the creation of observable types that provide notifications to clients when changes are made.
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System.Reflection.DispatchProxy. Provides a mechanism for dynamically creating proxy types that implement a specified interface and derive from a specified DispatchProxy type.
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System.Reflection.Metadata. Provides a highly-tuned, low-level ECMA-335 metadata reader. This is the same reader used by "Roslyn" C# and Visual Basic compilers to parse assemblies.
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System.Reflection.TypeExtensions. Provides extension methods for types in the System.Reflection namespace. These extensions are designed to be source-compatible with older reflection-based APIs.
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System.Resources.ReaderWriter. Provides classes for reading and writing resources in the system-default format.
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System.Runtime. Provides the fundamental primitives, classes, and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and exceptions.
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System.Runtime.Extensions. Provides commonly-used classes for performing mathematical functions, conversions, string comparisons, and querying environment information
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System.Runtime.Handles. Provides base classes, including CriticalHandle and SafeHandle, for types that represent operating system handles.
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System.Runtime.InteropServices. Provides types that support platform invoke (P/Invoke) and COM interop.
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System.Runtime.Numerics. Provides two useful numeric structures, BigInteger and Complex.
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System.Runtime.Serialization.Json. Provides classes for serializing objects to the JavaScript Object Notation (JSON) and for deserializing JSON data to objects.
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System.Runtime.Serialization.Primitives. Provides common types, including System.Runtime.Serialization.DataContractAttribute, for libraries that support data contract serialization.
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System.Runtime.Serialization.Xml. Provides classes for serializing objects to the Extensible Markup Language (XML) and deserializing XML data to objects.
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System.Security.SecureString. Provides support for accessing and modifying text that should be kept confidential.
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System.ServiceProcess.ServiceController. Provides the ServiceController class that represents a Windows service and allows you to connect to a running or stopped service, manipulate it, or get information about it.
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System.Text.Encoding.CodePages. Provides the ability to access existing encoding types for string manipulation across common cultural standards, as well as support to create custom Encoding Providers.
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System.Text.Encodings.Web. Provides support for encodings related to HTML, JavaScript, and URLs.
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System.Text.RegularExpressions. Provides a regular expression engine. The types in this library provide useful functionality for running common operations using regular expressions.
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System.Threading. Provides synchronization primitives used when writing multi-threaded and asynchronous code.
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System.Threading.Tasks. Provides types that simplify the work of writing concurrent and asynchronous code.
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System.Threading.Tasks.Dataflow. Provides a set of types that support actor/agent-oriented designs through primitives for in-process message passing, dataflow, and pipelining.
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System.Threading.Tasks.Parallel. Provides library-based data parallel replacements for common operations such as for loops, for each loops, and execution of a set of statements.
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System.Xml.ReaderWriter. Provides types for reading and writing streams of XML.
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System.Xml.XDocument. Provides XML-related types for querying XML documents using LINQ.
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System.Xml.XmlDocument. Provides types for manipulating an XML Document Object Model (DOM).
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System.Xml.XmlSerializer. Provides classes for serializing objects to XML and for deserializing XML data to objects.
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System.Xml.XPath. Provides classes that define a cursor model for navigating and editing XML information items as instances of the XQuery 1.0 and XPath 2.0 Data Model.
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System.Xml.XPath.XDocument. Provides extension methods that add System.Xml.XPath support to the System.Xml.XDocument package.
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System.Xml.XPath.XmlDocument. Provides extension methods that add System.Xml.XPath support to the System.Xml.XmlDocument package.
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Microsoft.CSharp. Provides support for compilation and code generation, including dynamic, using the C# language.
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Microsoft.VisualBasic. Provides types that support the Visual Basic runtime.
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Microsoft.Win32.Primitives. Provides common types supporting the implementation of Win32-based libraries.
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Microsoft.Win32.Registry. Provides support for accessing and modifying the Windows Registry.
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The overall list of items we currently plan to move onto GitHub is here.
.NET Core (including the corefx repo) is licensed under the MIT license.
.NET Core is a .NET Foundation project.
There are many .NET related projects on GitHub.
- The .NET home repo links to 100s of .NET projects, from Microsoft and the community.
- The .NET Core repo links to .NET Core related projects from Microsoft.
- The ASP.NET home repo is the best place to start learning about ASP.NET 5.
- dotnet.github.io is a good place to discover .NET Foundation projects.