I always find it fascinating how hard it can be to book a meeting or getaway with more than two people. Person A can these dates, person B can those dates, and person C can some other dates. Where does it overlap?
The idea is to have a simple site with a calendar. Someone starts an event and selects a few proposed dates, then enter the emails to the people who are invited (or if it’s a Facebook app, just select the friends). They can then accept the dates or propose their own. This can go on for a while. When everyone’s answered (at least once) an email is sent out to everybody with the dates that everyone can make it on.
My friend Torbjörn had a funny name name for this project: Meeteor, but it’s already taken. Any other suggestions?