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!
Wren - Offset your carbon footprint by saving rainforests
Splittable - Shared living made simple
Neutral - Offset your carbon emissions, right from your shopping cart
EquiTable - Split the bill fairly
Trip to Carbon - A carbon footprint calculation API for travel.