Splitwise - Splitwise is a free tool for friends and roommates to track bills and other shared expenses, so that everyone gets paid back. On the web, iPhone, and Android!
Tribeez - Flatshares, families, friends...
Kittysplit - The easiest way of sharing costs with a group of friends
ihatemoney - Manage your shared expenses, easily
Raft Calendar - A fun and beautiful calendar for couples and close friends
SplittyPie - Create event, add users and their expenses.