Mindmiester is a fairly basic tool that allows people to collaborate on mindmaps. The free version is limited but the academic version is a lot cheaper than Mindmanager. There are also some good example of mindmaps.
This is an awesome innovative presentation application. It works like Powerpoint and Keynote (as far as I can tell). I would like to recommend that this be explored with the view to making it *the* OP tool for HUM100 (and other Curtin units) as it could potentially, save a lot of angst and drama re upload and sharing issues!