While I have worked on open source software myself I'm, strangely, uncertain about how to cite it in a paper. I do know how to cite software itself, I'm just uncertain which author(s) to attribute it to.
I've got two programs to cite, one of which is a fork, with different copyrights over different files, not to mention the many unmentioned contributors to that work.
Do I just cop out and go "main contributor et. al"? And in the case of the fork, do I take the original author of the original software or the author of the fork?