Neat idea. Maybe its just figuring out whose website to host the project on. My guess is that Collaborator 1 would take the project on their website and give Collaborator 2 their cut. That takes a lot of trust. I don't really see a collaborating tool, so its more than likely going out and figuring out who would be interested in doing one. Working out ideas, pros and cons, setting up some type of contact/agreement, who is gonna host or how sell it together and give each party its dues.