microPledge looks like the most interesting effort to provide a platform for funding creation of public goods through donations that I’ve seen in awhile (which isn’t saying much). Their projects could be thought of as assurance contracts — you either get the software or your money back. Would be interesting to see them attempt to offer dominant assurance contracts — … or your money back, plus. They also have what looks to be a reasonable approaches to payments to creators while a project is in progress and quitting creators.
But the amounts pledged so far are micro.