git!

I (like many others) have started using git recently. It's pretty nice. Merging, which is difficult in CVS and SVN, is easier and more natural with git. If you look at the repository with gitk after doing some concurrent development, you'll see what I mean by merging being more natural.

git is still a little rough with the interface. It gives a lot of access which makes it powerful, but also gives more opportunities for confusion.

If you're coming from CVS or SVN, I recommend checking out the git glossary. Getting the git terminology figured out was a big help for me in learning git.

New Artisans also wrote a good document for learning git. In the 9th section, it explains how branches and merges aren't handled specially by git. If a commit has multiple children, it's a branch. If a commit has multiple parents, it's a merge.

Check out gitorious or github for online repository hosting. gitorious is focused on open source projects. github allows open source projects, but also offers private, paid repositories and has some nice visualization tools. github also hosts Rails.

So far no git support from Jira or Fisheye or any other tools like that that I know of, but hopefully it's soon on the way.