OpenBSD's source tree just turned 20 years old [marc.info]. The first improvements were for 32-bit sparc. It now supports 16 hardware platforms, with porting efforts on a few more. The project has now accumulated around 322,000 commits with an average of 44 commits/day by a cumulative total of around 356 hackers.
OpenBSD positions itself as a research operating system that takes a 'whole-system' development approach and stays withing the POSIX family. Disruptive innovation is encouraged and there are no qualms about removing unused or dangerous code.