Bazaar
Bazaar is a distributed revision control system. What does that really mean? A revision control system is a program that tracks how the source code of a program changes. It tracks what the specific change was, such as addition of a new piece of code, as well as who made the change. It also allows a developer to roll back to a previous version or create a branch to try out a new idea.
The second key piece about Bazaar is that it is distributed. Traditional revision control systems have a single place that the code is stored. Only certain people can access this place and change the code there. A distributed revision control system is different in that there is no single place that code is stored. Each branch that a developer is working on is equal, and they all take code from each other. This system is much like a number of equal merchants at a bazaar, hence the name.
Bazaar started out as a fork of the Arch distributed revision control system. A fork means that the developers disagree on where to take the program and break into different groups to work toward each group's different goals. However, Bazaar 2 was completely rewritten, as it was found that the current code did not work in the long term.