Ask HN: I'm a programmer with fintech experience. What business can I start?

I've spent my career at major banks doing things like pricing and low-latency trading. I'd like to now start a software business but I'm having a hard time with ideas. The ideas I tend to come up with...I have no domain knowledge in.

So now I'm wondering how to leverage my fintech experience to build something that can give me independence from a job. Payments? Financial analysis tools?