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!
Spliit - Free and Open Source Alternative to Splitwise. Share expenses with your friends and family.
ihatemoney - Manage your shared expenses, easily
Tricount - Manage and share expenses with friends
MoneyBuster - Multi-project shared budget manager able to sync with self hosted FOSS services
Kittysplit - The easiest way of sharing costs with a group of friends