The serial port stuff is very close to what I'm working on - what's on the other end of the connection? What does "integrating them into modern systems" look like for you: getting data out/pushing data in/both?

We typically integrate them by encapsulation. Building multiple layers of more modern systems for them to communicate through. A combination of Windows and Linux boxes. The other end of the connection is very old industrial equipment. This is not to run the equipment per se but to configure and program it.