I.O.U. Mate is described as 'I.O.U Mate is a free online tool that lets you track your debts (dinner splits, loaned books etc) with your friends and family. You can choose to track your debts privately or invite your friends to view and update your shared debts via a simple interface'. There are more than 25 alternatives to I.O.U. Mate, not only websites but also apps for a variety of platforms, including Android, iPhone, Android Tablet and iPad. The best alternative is Splitwise, which is free. Other great sites and apps similar to I.O.U. Mate are ihatemoney (Free, Open Source), SplittyPie (Free, Open Source), Kittysplit (Free) and Tricount (Free).
Going on a road trip? Worried about all the maths you gotta do to find out "who owes whom and how much" after the trip? Well, worry not! Add all your expenses to this app and let it do the calculations for you.
Cospend is a Nextcloud application to manage shared expenses in a group of people while staying in control of your personal data. It's easy to install (one click) in a Nextcloud instance and can be used with MoneyBuster, its Android client.
With this new shared living app, you can easily manage groceries, split bills, add calendar events and divide household chores. You can also use the integrated chat with polls to make planning even easier. OurFlat was made for anyone living with other people!