There are many source code management (SCM) systems out there, and since SCM is such an important part of development, the development of these systems will continue to happen.
Currently, there is a dominant system, however, and that system is Git.
Git has an interesting story: It was initiated by Linus Torvalds to move Linux kernel development from BitKeeper, which was a proprietary system used at the time. The license of BitKeeper changed, so it wasn't practical to use it for the kernel anymore.
Git therefore supports the fairly complicated workflow of Linux kernel development and is, at the base technical level, good enough for most organizations.
The primary benefit of Git versus older systems is that it is a distributed version control system (DVCS). There are many other distributed version control systems, but Git is the most pervasive...