I was surprised to see that I have not posted about revision control systems yet. I began using Subversion about a year ago for personal projects; it was a nice start, and I had my beloved server under my bed hosting my repositories for local access.
Since then, I have switched to Mercurial, which is so much more painless than Subversion, being distributed in nature, and the TortoiseHg Windows shell extension made it even more useful for me and my colleagues at the University.
Today, and for the past week or so, I have been watching the Pidgin Instant Messenger project, which uses the Monotone distributed version control system (DVCS). Monotone uses RSA keys (like SSH) to determine the identity of remote peers, and keeps its data in sqlite structures. It seems to be a very idealistic system, when it comes to version control, which is what I am always looking for.
Cruise over and have a look!
Registered Linux User #370740 (http://counter.li.org)