Ask HN: Open-source projects written in C

I'm trying to find open source projects written in C to contribute to. I'm not particular about the domain. I would be able to get into CAD/mathematical programming a bit more easily as that is what I'm working on currently, but that is not a requirement at all. I'm also interested in simulations, network programming and nifty Linux tools like terminal emulators, window managers (though I do not know much about them). Thanks in advance!