The IBM i operating system on the AS/400 is a system that runs on PPC for “midrange” systems. I did a bit of reading about it after seeing an AS/400 on ebay for $300, if I had a lot more spare time and energy I might have put in a bid for that if it didn’t look like it had been left out in the rain. It seems that AS/400 is not dead, there are cloud services available, here’s one that provides a VM with 2GM of RAM for “only EUR 251 monthly” [1], wow. I’m not qualified to comment on whether that’s good value, but I think it’s worth noting that a Linux VM running an AMD64 CPU with similar storage and the same RAM can be expected to cost about $10 per month.
There is also a free AS/400 cloud named pub400 [2], this is the type of thing I’d do if I had my own AS/400.