Chacun sa part is about managing shared expenses amongst a group of friends. You have holidays together, and you all pay bits of them along the way; house rental, gas for the trip, groceries, drinks, sun lotion… Chacun sa part helps reconciling these accounts. It keeps track of the expenses, and calculates who owes how much to whom.
Chacun sa part is a service written for fun by Roland Mas (and I also host the instance at chacunsapart.com, in case you're somewhere else). While I take pride in making things that work correctly, there's absolutely no guarantee or anything.
Should you feel the need to contact me, please send me an email at firstname.lastname@example.org.
For those who care about numbers: Chacun sa part currently knows about 4,000 expenses in 200 groups, involving 600 persons in total.