App for Submitting Expenses?

Does your chuch use a good app/tool for expense processing (e.g. Expensify, or similar)?

I'd like to use a modern tool with a phone app. But one thing that makes churches different than most businesses is that, in addition to staff, we also have many volunteers who might only submit an expense very occasionally. For staff it makes sense to pay for a system login and license. But for volunteers, we'd want a web-based way for them to submit occasional expenses (without requiring an app, login, or license). 

Any suggestions?