[nickh]

There're many solutions, from installable software such as Redmine[1] to hosted services such as TenderApp[2], GetSatisfaction[3], UserVoice[4], ZenDesk[5], FreshDesk[6], Groove[7], etc.

It all depends on what your needs are.

[1] http://www.redmine.org

[2] http://tenderapp.com

[3] http://getsatisfaction.com

[4] http://uservoice.com

[5] http://zendesk.com

[6] http://freshdesk.com

[7] http://groovehq.com