[Web4lib] Best web based Project Management Software

[Don Hamilton]

Hello, oft-read list!
 
I may be on the brink of off topic, but we are a team of five looking to manage projects in support of our ongoing evolution of digital library services.
 
I would like comments on web based project management tools you may have used to manage your projects.
 
Any really great ones? terrible ones? We'd prefer low-cost, and could host it ourselves if necessary.
 
Thanks in advance!
 
Don