Oikon is a simple expense tracking app. It's meant to do just that. No budgets, no complications. You open it, add your expense, and that's it, no wasting of time.
This is meant to be a complementary app for the iOS version (in order to facilitate reviewing expenses for a longer period of time), but it can be used without it.
Note: this app is free until June 14th, then a price will be associated with it.