Pretty much all online service APIs (Google APIs, Facebook and so on) out there are text-based.
Granted, JSON formatted text, but still absolutelly human readable text.
The reason for that is because it's agnostic of the machine architectures (stuff like endianess) on both sides.
The really crazy stuff in banking are the old binary protocols (like EDF) from the time when bandwidth was way less than now (so, the early 90s and earlier).
I mostly meant the base level shit with text files and ridiculous APIs. Converting from one servicing system to another sounds kind of fun, though. I've always enjoyed doing horrible things to data. The most recent one I heard is there's a drag and drop visual coding tool that I'm told can't export to apex - just make calls to it.