SIMH is a free and open source, multi-platform multi-system emulator.

SIMH was based on a much older systems emulator called MIMIC, which was written in the late 1960s at Applied Data Research.

[1] SIMH was started in 1993 with the purpose of preserving minicomputer hardware and software that was fading into obscurity.

[1] In May 2022, the MIT License of SIMH version 4 on GitHub was unilaterally modified by a contributor to make it no longer free software, by adding a clause that revokes the right to use any subsequent revisions of the software containing their contributions if modifications that "influence the behaviour of the disk access activities" are made.

The Open SIMH group cited that a "situation" had arisen in the project that compromised its principles.