I second this! A wiki is a great starting point for collaboration and collaborative documentation. My experience with collaboration is that > 90% of the issues are issues with people, not issues with technology. Getting people to actually share consistently, organize themselves, etc is the real battle--if they are motivated and organized, I don't think it matters much what tool you use, it'll get done. If they are not motivated and organized, it doesn't matter how nice of a system you build for them, they won't use it and it will be a waste of time and resources.
If by some chance you do have a spectacular group of collaborators, and after using a wiki for a while they complain about missing features, then you might look into writing extensions or perhaps moving to something richer.