Watcom C
The Watcom C language and compiler was really popular in the early 1990's because of its optimizations for the Pentium CPU, along with its ability to target MS-DOS, Windows 3.1, OS/2 in both 16bit and 32bit flavors. Watcom C also added the ability to target Novell Netware. Watcom C includes both register & stack calling compilers, which depending on the targeted CPU can yield better results.
7.0
I've been able to find some information on Dr. Dobbs magazine, detailing how version 7.0 introduced a 386 32bit specific version with support of Phar Lap's 386|DOS-Extender and Eclipse Computer Solutions' OS/ 386 extenders. Novell Netware 386 (which later became Netware 3) was also based on Watcom 7.
8.0
8.5
Released in 1991? Adds support for Windows 3.x?
9.0
Included support for OS/2 2.0, DOS & DOS 32bit This release was more 'combined' unlike 8.
10.0
This version bundled the popular DOS/4GW dos extender, and was made popular by such games as Doom. Version 10.0 included the Win32 SDK for Win32s & Windows NT 3.1, the Windows 3.1 SDK, and the OS/2 1.3 & 2.0 SDK's for OS/2 development. Additionally it included the MFC libraries.
11.0
This updated the Windows NT support up to 3.5, and Windows 95 levels.
OpenWatcom
Watcom sold all the compiler technology to Sybase where it languashed, then it was swept up by Powersoft. It was then opensourced, and is free to all including its FORTRAN.
The current version is 1.9
