Coherent is a clone of the Unix operating system for IBM PC compatibles and other microcomputers, developed and sold by the now-defunct Mark Williams Company (MWC).

If it came to it, I could never honestly testify [...] that what they generated was irreproducible from the manual.Much of the operating system was written by alumni from the University of Waterloo: Tom Duff, Dave Conroy, Randall Howard, Johann George, and Trevor John Thompson.

[3] Coherent was originally written for the PDP-11 range of minicomputers in 1980, then ported to various early 1980s microcomputer systems including IBM PC compatibles and machines based on the Zilog Z8000 and Motorola 68000.

[5] In 1985 it criticized the difficulty of installation, but stated that "as a UNIX clone, Coherent is amazingly complete ... it should be easy to port programs ... the price of $495 is a bargain".

[6] Early 1990s reviews of Coherent pointed out that the system was much smaller than other contemporary Unix offerings, as well as less expensive at US$99.95, but lacking in functionality[7] and software support.

[7] A review in the AUUG's newsletter was more positive, favorably comparing Coherent to MKS Toolkit, Minix and Xenix, and suggesting it might fill a niche as a low-end training platform.