[Philomath]

You can give a try at Redmine. I've used it and I think the differences might be pros for some and cons for others. The UI is, in my opinion, bad, and it lacks some features from Jira. That being said, since it's open source (coded in Ruby), you can personalize it, add your own features (or others that are already out there) and host it yourself. At the same time there's a lot of hosting companies that do that for you if you don't want to play this kind of game. Using hosting services usually makes it a lot more complex to add your own features though!

[mister_hn]

+1 for Redmine, as it can be self-hosted and doesn't need to hand out your information to SaaS ones like Trello or Taiga

[majewsky]

Taiga is open-source and can be self-hosted.