Splitit is a very simple app for keeping track of shared expenses. It is meant for people who split expenses such as groceries, bills and rent with a significant other or roommates. It will allow you to see who owes who what amount for a given time period so it's easy to square things up at the end of that time. It assumes each user pays for items then other users owe that user (optionally - items don't have to be split). It is not meant as a budgeting tool.
Now create some users:
rake create_user login=chris password=mypassword
Start up the server locally:
Your app should be running at http://localhost:3000
After logging in, create some categories for receipts you'll be entering.
Each user should enter their expenses (called receipts), and what percentage of the cost the others are responsible for. With just one other person, you would simply enter %50, meaning for that item, that person owes you half the cost. If you buy something for someone and they will be paying you back in full, you would enter 100%.
Once you want to see how much you owe everyone and how much they owe you, go to 'report' from the receipts listing.