Wacky Wheels (1994): Most likely inspired by Super Mario Kart, this game is a kart racer for the PC. That means the controls are simple, the physics very arcade-like, and the courses range from the practical to the incredibly unrealistic. Like Mario Kart, it featured a variety of weapons you could pick up to temporarily spin-out your opponents. But it had a few unique touches of its own, including a mode where you loaded up on weapons and chased after ducks on an enclosed course. While it may have trouble keeping pace with modern games like Mario Kart Wii, this is still pretty fun. It remains shareware, and can be downloaded from...

Wacky Wheels: http://www.3drealms.com/wacky/ 

Balls of Steel (1997): Essentially a pinball game with a variety of tables to play on, this may not be everyone’s interest. But if you’d like to see the game that spawned the Ventrilo harassment fad of annoying people with clips of Duke Nukem’s voice actor saying “I’ve got balls of steel!”, here it is.

Balls of Steel: http://www.3drealms.com/balls/index.html

Most of the above games have been published under Apogee’s name, with Pinball Wizards being the brand for Balls of Steel. But a pair of games published under the actual 3D Realms brand name stand out.