Advanced Gravis Computer Technology, known as Advanced Gravis or merely as Gravis, was the forerunner in developing non-joystick game controllers for the PC
Most notable was the Gravis Gamepad. The Gamepad was a knock-off of the Super Nintendo controller design, distinguished by an ergonomic "bone" shape and 4 colored buttons (without the two shoulder buttons). It used the standard Joystick Port format (which appears to be a smaller parallel port, and which was usually a facet of old sound cards) Later, the gamepad was also developed for the Mac and Amiga formats.
Unique to the gamepad was the ability to flip a switch on the top of the controller and toggle the handedness of the controller (a clever function rarely implemented in console or pc controller designs). Also, another switch allowed the 4 buttons to be turned into a 2 button controller with a rapid fire mode.
The Gravis Gamepad was ideal for non-flight sim games, as it's d-pad is digital and not analog. Side-scrolling platformers, (pre-mouselook) First Person Shooters and other games that don't require precise and varying range of movements.
Some games for which the Gravis Gamepad was perfect:
Advanced Gravis (in conjunction with budget PC peripheral manufacturer Kensington) is still developing joysticks and gamepads based on popular console designs.