Random thought I had about the current WCG XRP giveaway that Ripple Labs is sponsoring. Why not have a Bitcoin-like currency that is just always mined via Boinc? Gridcoin almost did this, except there they give you a bonus to your ordinary search-for-hashes-with-your-GPU mining, rather than just awarding coins based on Boinc solutions. Why not just tie it directly to Boinc, and dispense with the crypto mining altogether?
Ripple's almost doing that, but again, this is just a temporary promotion they're doing. Why not make it permanent?
I think there's a desire for proof-of-work based coins that use a different proof-of-work -- i.e., not SHA-256 or scrypt -- which has been part of the success of Primecoin. Also, finding prime numbers is vaguely useful. But Boinc is useful in a much more concrete way, plus anyone can get it running because the client is easy to use, unlike, say, cgminer, which is quite difficult to set up.
I'm a developer and have been thinking it would be a fun project to build an altcoin that works this way. I have not built a coin before, but hey, there is a first time for everything, right?