Fiwix
A UNIX-like kernel for the i386 architecture
...It basically comprises a Fiwix kernel, GNU tools, libraries and additional software. All the included software is free and open-source software made available both as compiled binaries and in source code form, which allows modifications to the original software.
FiwixOS 3 uses the Newlib v3.1.0 as its C standard library, and the Ext2 as its primary file system.
Fiwix is an operating system kernel written from scratch, based on the UNIX architecture and fully focused on being POSIX compatible. It is designed and developed mainly as a hobby OS and, since it serves also for educational purposes, the kernel code is kept as simple as possible for the benefit of students and OS enthusiasts. ...