A free Windows-compatible Operating System

Simple and portable (but not inflexible) GUI library in C that uses the native GUI technologies of each platform it supports.

Lightweight Ruby

XLibre Xserver

The fastest JSON library in C

Darwin is the Open Source core of macOS, and PureDarwin is a community project to extend Darwin into a complete, usable operating system.

Portable C standard library

Automatic conversion of the NetBSD src CVS module, use with care. Please submit bugs/changes via https://gnats.netbsd.org

Minos is a mini operating system written in C

An ELF loader for embedded systems.

Fast linear algebra and math library for the Hitachi SuperH4 Processor (used by the Sega Dreamcast).

Retro Rocket BASIC Powered Operating System

Switch between two running operating systems without losing their state.

A free Windows-compatible Operating System

A free Windows-compatible Operating System

Freestanding 64-bit Operating System

OpenSSL static library build for x86/x64 - MSVC/MinGW

PrettyOS