RedMine

​RedMine is the latest incarnation of the Trac clones written on top of Ruby on Rails. It is released under the GPL. Much more successful than the late ​Collaboa (discontinued), it's getting more and more popular.

And there are indeed lots of good ideas that we could now "steal back" in Trac, in one form or the other: multi-project support (#11025), ticket progress bar (#1084, a long time favorite of mine I never got around implementing), ticket comment editing (#454), bulk ticket changes (#525), etc.

And let's not forget ticket dependencies (#31), very important!

Also the Ruby-based ​ChiliProject has been ​discontinued in February 2015.