I think that's how Krita (a painting app) pays the bills. The code is GPL, and most Linux distros package it for free. But on the windows store, they have a for

I think that's how Krita (a painting app) pays the bills. The code is GPL, and most Linux distros package it for free. But on the windows store, they have a for pay version for some relatively low price (€25 or such). It's not a billion dollar business like Photoshop, but apparently it pays the salary for a few full time employees.