OpenGL ES. Graphisme. Objective-C. Cocoa. Xcode. Librairies. Tags. Another common version control concept is a tag.
A tag is just a “snapshot” of a project in time. In Subversion, this idea already seems to be everywhere. Each repository revision is exactly that—a snapshot of the filesystem after each commit. However, people often want to give more human-friendly names to tags, like release-1.0. And they want to make snapshots of smaller subdirectories of the filesystem.