Redmine

+1. You could go further I think with little trouble. You could have auto generated tags that signify the project/subproject something is in (to mimic namespaces). In JSPWiki for example, people assign to something like category [Computing.Programming.Python].

In Redmine's, case, it would be nice to do

[Project:MainProjectA.SubprojectB] [Project:ProjectC.SubprojectD] [IssueCategory:SomeIssueCategory]

the syntax would have to be hashed out a bit. If issue categories could be inherited, then you could point to a top level projecct's issue. auto-tagging would really help people see sets of pages as they want w/o differentiating filtering by tags vs some database property.

-Dave