At a previous job I deployed MediaWiki in order to provide our workgroup with a collaborative memory, which somewhere along the way developed into a inventory management too, life cycle planning tool and crude ticketing system.

A very sharing fellow showed me Request Tracker, an open source ticketing tool which does a lot of things better than we used to.  There is a standard version and a version optimized for incident response teams.  Both versions look mature and run on Unix/Linux operating systems.