... then you must enjoy this classic: http://www.coboloncogs.org/INDEX.HTM

I've toyed with the idea of setting up mainframes-as-a-service. I would probably just run the various Linux distributions running inside Hercules and abstract it away as cleanly as possible. You'd never get the performance or capacity, but you'd get a cheap, easy emulation for coding and small-scale testing. It's been a while since I had time for a side-project but I'd still love to work on this.