Feature/test tracking

I work at a small software company (5-10 developers), and we''re trying to find a system (preferably free/opensource) to track features and associate them with spec data/informal test cases, holding information for each feature such as when it was last tested or reviewed and by whom. A heirarchical model would be a big plus, so high level features could be made up of smaller subfeatures. Does anyone know of any systems that do things like this? Something like bugzilla would probably be workable, but it would be nice to get something that actually supports heirarchies, and is made more with testing than bug tracking in mind. Thanks!