Free Version Control System – Bazaar
Bazaar is a free version control system for tracking project history over time and collaborating easily with other team members.
Whether you are a single developer or a group of developers (at the same location or working remotely) Bazaar does the job well.
It is an easy to learn and use system which can work on all major OSs. Also, compared to Git and Mercurial, it supports bound branches (an easier and safer way of implementing a centralized workflow).
There are many applications that can work with Bazaar like Loggerhead, a web interface for it or several IDE integrations.