The ISA bus was really a very approachable way to add hardware to a system. I worked at a place where a couple of electrical engineers wanted to build a bridge

The ISA bus was really a very approachable way to add hardware to a system. I worked at a place where a couple of electrical engineers wanted to build a bridge from a PC to a specialized industrial control network. So, with very little knowledge of computer programming (they were low level guys) or bus technologies they banged out an ISA card and an application to throw bytes out onto the network. Since ISA cards basically just showed up in memory space you just told the application they wrote which chunk of memory it was using and the application wrote to a specific offset to write data to the network and read from another offset to see what came back in. They had a pretty successful little business from that idea. And those cards were STILL selling pretty well into the early 00's--I think they sold them until 2008. Of course the application was never updated and you couldn't just write to random memory locations post Windows 95...so thats the only OS (and DOS) that I ever saw that card run on.