pyvm is an experimental python virtual machine with a compiler written in python. pyvm is very incomplete and does not care about backwards compatibility so you shouldn't use it unless:
In this release pyvm has real lightweight threads (co-routines). That is that there are two OS threads, one running the main interpreter loop and another one polling for file descriptors. When there is a blocking system call, the main interpreter thread passes a request to the polling thread and removes the co-routines from the running list. With this setup, pyvm can run unlimited python threads with just two OS threads.