This is actually several separate C++11/C++14 libraries:

1. "date.h" is a header-only library which builds upon <chrono>. It adds some new duration types, and new time_point types. It also adds "field" types such as year_month_day which is a struct {year, month, day}. And it provides convenient means to convert between the "field" types and the time_point types. See http://howardhinnant.github.io/date/date.html for more details.

   Here is the Cppcon 2015 presentation on date.h: https://www.youtube.com/watch?v=tzyGjOm8AKo

   Here are the Cppcon 2015 slides on date.h: http://schd.ws/hosted_files/cppcon2015/43/hinnant_dates.pdf

2. "tz.h" / "tz.cpp" are a timezone library built on top of the "date.h" library. This timezone library is a complete parser of the IANA timezone database. It provides for an easy way to access all of the data in this database, using the types from "date.h" and <chrono>. The IANA database also includes data on leap seconds, and this library provides utilities to compute with that information as well. See http://howardhinnant.github.io/date/tz.html for more details.

3. "iso_week.h" is a header-only library built on top of the "date.h" library which implements the ISO week date calendar. See http://howardhinnant.github.io/date/iso_week.html for more details.

4. "julian.h" is a header-only library built on top of the "date.h" library which implements a proleptic Julian calendar which is fully interoperable with everything above. See http://howardhinnant.github.io/date/julian.html for more details.

5. "islamic.h" is a header-only library built on top of the "date.h" library which implements a proleptic Islamic calendar which is fully interoperable with everything above. See http://howardhinnant.github.io/date/islamic.html for more details.

There has been a recent change in the library design. If you are trying to migrate from the previous design, rename day_point to sys_days everywhere, and that ought to bring the number of errors down to a small roar.

"date.h" and "tz.h" are now proposed for standardization here: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0355r0.html