Not affiliated in any way with Actual Budget, but I can't recommend it enough. It's the FOSS version of YNAB pretty much so if you're a fan of envelope budgeting it's a great tool. I'd even say it has quite a few other strengths compared to YNAB (free bank syncing in the EU with more banks supported for example), and you can always be sure that your financial data stays within your reach.
I wish they would of pursued a business plan. I feel like we need some software for small business that isn't run by a huge company ready to screw you over.
The original author tried to turn it into a business. Turns out that was next to impossible up against YNAB. Gave it to the community who’s keeping it current.
If one doesn't want to self-host it one can always go through a service like PikaPods who do in fact have a revenue sharing deal with Actual Budget. And either way, Actual Budget isn't really an accounting tool for businesses, or did I misunderstand you?
Depending on the size of your mom and pop, I think it would do much of it. At least keep things organized to do a demo of QuickBooks or give to an accountant.