Over the past few years a new system called Git has been developed (by Linus Torvalds and other Linux developers) for use in distributed, non-linear development projects.
These days, a lot of iOS development projects are using multiple developers scattered all over, and a SCM system is absolutely necessary for there projects. We'd like to use Git, but Apple doesn't support it yet. Xcode 4 is supposed to.
If you're on a Mac, and if you do iOS development you are, you can find a good, free Git client called GitX. It has the following features, several of which are Mac-specific:
- Detailed history viewer
- Nice commit GUI, allowing hunk- and line-wise staging
- Fast workflow
- Explore tree of any revision
- Nice Aqua interface
- Paste commits to gist.github.com
- QuickLook integration
[crarko adds: I'm part of a development team working on an iOS project. We're probably going to be using Subversion for our first release or two, but I'd like to move to Git. This is the client software I'm trying out, but I'd like to hear what others are using. Xcode 4, when it is released, should make the move easier. There is no date set for that yet.]

