Do you have an idea? Whether AlternativeTo nor OpenSourceAlternativeTo got an answer.
EDIT: I should have had added, that I was not looking for the financial aspects of the app, but I was looking for a possibility to store tickets and cards: Catima offers at least somewhat, what I was looking for.
Unfortunately AFAIK there are no open source projects that major credit card vendors and banks are willing to work with. That’s the fault of the banks and cc vendors, not the vendor you are shopping at of course.
You might be interested in strike. It’s not open-source but it’s built on open-source protocols: