I was a big fan of BitKeeper when it was free for open source development, and I still miss a number of it's features. Oh well. At this point however it's place in my heart has been replaced with SVN and further SVK.  SVK allows for one of the things I miss the most, decentralized version control. With SVN I was commonly frustrated when I wanted to push back code but wasn't:

• online
• finished

I commonly found myself in the position of having code that I was done with, or having made some changes I was (at least relatively) sure about and needing/wanting to commit.  With the goal being to move on to another change, modification or new function. Sometimes being quite sure that what I really wanted to do was poke around but not have to worry about taking a snapshot of the current code to get back to it after I took a horribly wrong approach.

SVK fills that void, by using SVN as a base but keeping a local copy and allowing mirroring and syncronization I can commit at will effectively check pointing code whenever I think I have completed something or when I know I am about to go off the rails with some wild idea.

SVK also makes rapid development/testing easier, since the workspace in SVK is a flat filesystem using rsync to push changes to a test system is quite effective without the  overhead of copying the local .svn structure to the test host.

A bit more on mirroring particularly CVS later.
See also: The SVK Wiki, The  Subversion Project Page

Technorati Tags: SVK, SVN, CVS, SCM