I'm not sure I understand your concern about selling the software. It's perfectly common to sell software libraries and frameworks on a recurring license basis.

I'm not sure I understand your concern about selling the software. It's perfectly common to sell software libraries and frameworks on a recurring license basis. The fact that you need to supply the source shouldn't be an issue; either practically or from a risk perspective. What do you mean by complexity in licensing? Do you mean that you don't own all the IP for the software? In which case, yeah, you're likely to struggle. Similarly if some or all is GPL'd (or similar) and the usage model implies a derivative work, that's probably not going to fly either. I can't see any benefit to you in open sourcing wrt selling to financial institutions. You absolutely can go that route but, if you're happy to sell directly, that's will require less work from the customer side. Also, even if you're not finished yet, if you have contacts who are genuinely interested in the work, have you thought about asking them to fund the completion? We've done that in the past, and I worked for a startup that had their first client pay them to complete the offering. The nice thing about that approach is that they're often not proprietary about it. As in, they're happy for you to sell to their competitors as it spreads the risk around.