The Roundup Bug Tracker

Roundup is a highly customizable Bug Tracker (and more...) written in Python.

It is somewhat older than Trac, and some people think it's more mature in some areas (like E-Mail integration). Instead of Clearsilver or Genshi it uses TAL/METAL (known from Zope) as a template language.

In some projects both trac and Roundup are used; Roundup can be customized to support trac-style [wiki:...] links to a trac portal.

There's also a Wiki for Roundup customization and mailing lists for users and developers.