What do you want/need from a bug tracking system?
moe: A crossbreed between MantisBT (search/filtering power, subtickets/ticket-trees, "direct feel"), redmine (Interface cleanlyness, Gantt-Charts, SCM integration) and perhaps PivotalTracker (Ease of use, the "velocity" idea).I could write a book about what rocks and sucks for each, but the take-home is that neither does everything right.My main suggestion would be: Make it as modular as you can. This is imho the holy grail of such a system.Example: When I don't use time-tracking then I don't want to see these buttons in the UI. Make sure "time-tracking" is a self-contained module that can be unloaded and not a series of conditionals in your codebase.The goal should be to have a a very slim core with a plugin-system so powerful and easy that people will start writing the interesting features for you. Everything should be a plugin.