Thanks for providing some information from your side, Alex. Personally I think it was a mistake to sell this software. If it was difficult for you to earn money with it, it will be even more difficult for other people. Maintaining and developing code that others have written is certainly not easier than maintaining your own code. I can imagine that the new owner had good intentions but then realized how big the task was, became demotivated and gave up. You should have kept it, but slowed down development.
I't sad that the whole story wasn't a success for you, since I believe the original idea of Freeter is great, I haven't seen anything similar in the market, and your software implementation is also very well done.
Maybe you can sit down with the new owner and find a way to sort out the mess and make the whole thing work again.