KolibriOS is an operating system (OS) for x86 PCs. It was originally a MenuetOS distribution, with some improvements, by a Russian developer team. It has now become a MenuetOS fork project, by the KolibriOS Team. Both OSs are written in the Assembly programming language FASM. But C, Free Pascal, and Forth can be used for user programs. KolibriOS has a GNU General Public License, so it is free, open source software.