HeliOS is an operating system initially developed for the RISC-V ISA. It currently targets QEMU, but in the future it is intended that it run on real boards/computers. It is developed mainly in C and C++, but additional support for other languages (such as Rust) might be added in the future. It is still on its baby-steps, thus it doens't do much.
The project currently doesn't accept contributions nor is looking for that (but it is open to suggestions/mentorship), given the way it is being developed (through sheer experimentation).
Building is currently done through a Debian Linux container, which already contains the necessary environment to build the kernel. If you want to do it locally, you can analize the files under .github.
Running the kernel is supported on QEMU and on the Starfive Visionfive 2 board.
To run it on QEMU, you simply have to run ./script.sh. Be aware that you must have u-boot SPL as the bios/firmware for QEMU to run it. Instructions are provided at u-boot's github on how to. Then, when the u-boot prompt shows up, you type in:
$> load scsi 0:1 0x84000000 /boot/helios.bin
$> go 0x84000000 --fdt ${fdtcontroladdr}