Where can I find good collaboration tool?

Question

I'm working on a project where I'm using mindmeister.com as a tool when brainstorming new ideas.

Now I need a tool where I can define roles and what responsibilities they have, and link this to a person / persons. It would also be nice if I could add tasks with a due date for each person.

Are there any open source websites which has this?

PS.

The tool must be light weight, and not strictly for programmers only.
Main usage would be before development stage.

Update
Ok, after some more thinking, it looks like I need some kind of project template tool.

I have this project. In order to be succesfull, I need to cover task A, B and C. Task A has sub tasks like a1, a2 and a3.

Now this is still just descriptions of things I must think of / answer, in order to have a successful project.

When those Qs have ben answered, I can start delegating tasks to project members which again can break down the tasks.

Answer 1

I personally like Trac - it is a lightweight wiki and issue tracking tool.

Answer 2

GanttProject is good for breaking down project responsibilities to persons and defining timelines.

Answer 3

Collabtive is the best one I've used. I think it should cover the functionality you're asking for. They also offer hosting for reasonable prices.

DotProject is also an alternative, but without the good looks...

Answer 4

Redmine is great.