It used to amuse me to run a test Novell server from a DOS session in OS/2, and then connect to it from the Novell Client for OS/2, such that I had a full blown client/server implementation for testing with all on the same machine. And this was on a 486DX/2-50. I forget how much RAM it had. I think I had maxed out the board at 64MB RAM.
I'll take it back a little further yet :) A good friend of mine and myself used to run a BBS system (the ollld dial-up-with-modem type). It started off on a single DOS-based PC. We quickly maxed out the two IDE drive slots. Eventually he expanded it with Lantastic, networked it to two other DOS machines, a Win31 machine, and shortly after, OS/2 Warp became the BBS 'server,' running Lantastic for OS2. That was the most awe-inspiring thing back then, having one program running in DOS-mode, and still be able to alt-tab away (and the process didn't suspend, like Win31 did!) and play a game, or do anything else you wanted.