If you played video games on DOS in the 1990s and saw the output starting with "DOS/4GW" before the game took over the graphics hardware, the game developers had been using Watcom (before it became OpenWatcom).
Also, DOS/4GW, the extender included with with Watcom C was just a cut-down, sub-licensed version of DOS/4G by Rational. The proliferation of the Watcom/DOS/4G combo was because it was out there the earliest.
If you played video games on DOS in the 1990s and saw the output starting with "DOS/4GW" before the game took over the graphics hardware, the game developers had been using Watcom (before it became OpenWatcom).