I wrote a data recovery POSIX compliant command line app in C in 2003 that runs under OS X, Windows, and linux. It's still selling well, and has been all these years. Over time it's generated millions in revenue as it's been used by several different competing apps, and I have only recompiled it about twice in the last 15 years, each time only making a (very) minor change. It went a good decade without a recompile and continued selling well and being widely used.
The reason I'm happy to say this publicly is because
a) it took years to write, full time. Data recovery is a hell of a lot more complex then I'd ever imagined.
b) data recovery is no longer possible on SSD's (if they have TRIM enabled, as they do in all major OS's) so it's a declining market. Anyone would be nuts to be trying to enter it at this point.