I have been trying to find the same thing. I'm currently using Curio on the Mac to try to do bigger picture layouts (mind maps especially). It supports project-centric development too, though I've not taken steps in this direction with it, and Curio only integrates in a limited way with iCal.
You might get helpful info from this site ...
http://en.wikipedia.org/wiki/List_of...pping_software
I'd like to hear how you make out with the search.