I'm not sure if many rowers are also programmers, but I'm building a rowing app making $0 per month.

iOS only for now: https://apps.apple.com/ie/app/oxun/id1624866789

Works with any Bluetooth rowing machine (WaterRower etc), currently building support for Concept2 PM5 machines. It's one of the few apps that allows you to row indoors and outdoors.

Cheers!