I specialize in bringing ancient DOS and early Windows xBase apps into modern Windows. There are zillions such apps still out there.
It just took me several hours to determine what language an app for a new client was written in (Delphi 2.) Further complicating matters, the original programmer apparently got real clever and changed the header info in the DBF file to something inscrutable so it could not be opened outside the app.
My mission, should I choose to accept: Twiddle with the DBF header info until it opens in FoxPro,at which point I write a middleware app to feed it data from elsewhere.
I do same kinds of things with Clipper and FoxDOS apps, often converting the entire app to Visual FoxPro. These apps often perform mission-critical tasks at good-sized companies too.
The puzzle aspect of this can be fun. This Delphi app took a while to deconstruct. (And yes, it runs a major part of their business.)