DOS extender
The DOS extender was arguably invented by Phar Lap, but it was Tenberry Software's (formerly Rational Systems) 386 extender DOS/4GW that brought protected mode DOS programs to a mass market. Included with Watcom's C, C++, and Fortran compilers for 386 class processors, it soon became a ubiquitous mainstay of PC applications and games such as id Software's successful "Doom".