This was something I didn't expect, but it's possible to use Xcode with TFS (Team Foundation Server) to store and share your projects.
Of course, TFS support is built right into Visual Studio, which means that even with Express editions you can sign up for a free TFS account, and use it as a remote source code repository. Using a source code management system is the sign that you've migrated to being a Grown Up Developer, and it is just vital if you are working on a team. The fact that you can get a TFS account that supports up to five users for free means you're just nuts if you don't even give it a try. If you've a laptop and a desktop computer, and need access to your source code on both, or if you're working with a buddy on a project, or if you've ever felt the shame of losing the code to a particular release in the swamp of your desktop folders, then you need to do this. I'm not kidding. And it's not even hard to do.
So, first of all, sign up for a TFS account here: http://tfs.visualstudio.com
If you are developing Windows / Windows Phones apps, that's pretty much all you need to do. You can easily check in and check out projects from inside Visual Studio. For a good guide on what that actually means, and how it's going to make your life SO much easier see here.
If you want to use TFS to store your Xcode projects, then check out the guide here. Now, there are some caveats. You can store your Xcode project in TFS and pull it down to a different computer, but Xcode will not automatically push updates into the TFS, only to the local repository. That said, there are some command line tools that will do this for you - specifically "Git-tf", This means you work as usual in Xcode, and then go to Terminal to push the changes to TFS when you want to make a commit. You can even automate builds, using Jenkins and for information on setting this up, see this excellent blog post.