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!
Monzia - Monzia can help you save money, relieve stress and make time for the fun things in life.
Memodude - Memodude keeps track of who you lent to, reduces your receivables and gets rid of bad payers.
Grisbi - Accounting for everyone !
WieBetaaltWat - With WieBetaaltWat you can manage a list with your shared expenses.
Ledger-cli.org - Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line.