1. PowerPC and S390(X) — big-endian-architecture, for them there are a lot of Linux. Although it is not certain whether under them Mono.
2. With virtualname tight. I met a simulator for PowerPC, S390 and S390X. With the first (name not remembered) my relationship didn't work out because I did not wait for the completion of the upgrade process gentosha repository (Gentoo there comes in as a main system) — three days it is not enough. For S390/S390X used Hercules: there are things more fun, even managed to do something useful, but the setting is quite complicated, the documentation is actively used specific terminology without any explanation, a window the path is the height of inconvenience, the speed leaves much to be desired, and about any desktop environment on the guest you can just forget it. I don't remember whether it supports Hercules graphics modes, but even if it does, there are hundreds of simulated kilohertz for them is clearly not enough.
Naturally, neither on PPC nor on S390 any Windows are not put — it does not exist in nature. Only nixuya system.