Bugs Everywhere (BE) is a bugtracker built on distributed version control. It works with Arch, Bazaar, Darcs, Git, Mercurial, and Monotone at the moment, but is easily extensible. It can also function with no VCS at all.
The idea is to package the bug information with the source code, so that bugs can be marked “fixed” in the branches that fix them. Other architectures—such as keeping all the bugs in their own branch—are also possible.