Is there a issue tracking system with hierarchy for tasks?
It's pretty obvious taht new-feature-request can be split into more parts (UI change, Bac office-change).
Also bug-solving can be split into multyple tasks.
Is there any tracking system that supports that?
Edit: Any free system
Most of the current issue tracking systems do.
Off the top of my head, Bugzilla, FogBugz, Trac, and Jira all do.