Back in the 80s and 90s, 3D Realms was better known as Apogee Software, a leading publisher of PC shareware games. The idea was that you would get the first part of the game either for free or very inexpensively, and if you liked what you saw, you could buy the rest of it. Unlike a demo, a shareware release was usually a significant fraction of the game, about twenty-five percent of it. This was the model that Doom and Quake were distributed on, and it was quite successful for a time. There were games in just about every genre; first person shooters, 2D platformers, puzzle, even complex sci-fi flight ’sims.’ A selection of Apogee’s games using the shareware model is included below. 

Duke Nukem 1 (1991) and 2 (1993): These two are all about old-school 2D action. A man, a gun, lots of platforms and enemies, and one goal: Kill. Like most games of its time, the plot was not very deep and mostly served as an excuse for the player to have Duke shoot tons of monsters on his way to the exit of each stage. He could gain powerups to make his gun stronger or fire different kinds of projectile, refill his health, and do all sorts of other things you’d expect from similar 8-bit NES games of the time. While the graphics in the original Duke Nukem have aged poorly, the sequel still looks okay, and both are pretty fun.

You can download Duke Nukem 1 and 2’s shareware episodes from: 

Duke Nukem 1: http://www.3drealms.com/duke1/ 

Duke Nukem 2: http://www.3drealms.com/duke2/ 

Bio Menace (1993): Essentially in the same genre as Duke Nukem 1 and 2, this game is given its own entry to get your attention for one thing: It’s free. The whole game was released as freeware. You can get it at:

Bio Menace: http://www.3drealms.com/menace/