Open SIMH
SIMH is a very popular framework and collection of computer system simulators.
SIMH was created by Bob Supnik, originally at Digital Equipment Corporation, and extended by contributions of many other people. It is now an open source project, licensed under an MIT open source license and moderated and maintained by members of the SIMH Steering Group
The Open SIMH simulators package is located here: https://github.com/open-simh/
I strongly encourage anyone interested in Computer History and Computer Simulations to look and this very worthwhile project (and even get involved)!
Also check out the SIMH mailing list at https://groups.io/g/SIMH