What are some alternatives?
When comparing BillMonk and WieBetaaltWat, you can also consider the following products
SplittyPie - Create event, add users and their expenses.
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!
TabSplit - TabSplit allows users to keep track of their "social debts".
Kittysplit - The easiest way of sharing costs with a group of friends
ihatemoney - Manage your shared expenses, easily
Tabbt - Tabbt takes the hassle out of handling money among friends.