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!
Halfdollar - Free and elaborate spreadsheet budgeting.
Kittysplit - The easiest way of sharing costs with a group of friends
Budgy 2 - Your best free budget assistant on the go
ihatemoney - Manage your shared expenses, easily
Budgt - Track your ramen spending (iOS)