Yeah, my interest in vintage systems - the C64 particularly, but even old Macs, old minis, etc. - isn't games either (though candidly it wasn't my interest really back in the day as well). It's the challenge of making it do things that are interesting by modern standards. It's Turing-complete, so anything should be possible ... ;)
A while back I started writing an assembly language sha256 algorithm for the C128. It's basically a lot of adds and bitwise operations on 32-bit values, which gets really tedious when you have to do them 8 bits at a time, carrying/shifting through a set of 4 bytes. I should finish it to find out how many hours it takes to process a decent-sized file.
