Kiwi is my hobby operating system project which I have been working on since around half way through 2009. It is written in C and assembly, as well as C++ for parts of userspace. It currently supports 64-bit x86 PCs, though the kernel is designed to be portable to other architectures.
The older master branch in the Git repository features a simple GUI and is capable of running various pieces of UNIX software such as Bash. The redesign branch of the Git repository is the current main development focus, and is a redesign of major parts of the system, focussed on improving the API exposed by the kernel.