From Sega Retro
Zero Tolerance is a first person shooter developed by Technopop and Accolade and published by Accolade for the Sega Mega Drive in 1994. It is notable for being one of the few first person shooters available for the system, a demanding genre seen by many to be outside the capabilities of the Mega Drive's hardware.
Gameplay in Zero Tolerance is similar to other first person shooters of the era, with the player controlling one of several characters navigating map from a third-person perspective, shooting enemies while trying to find an exit. In terms of technology, Zero Tolerance lies somewhere between 1992's Wolfenstein 3D and 1993's Doom - rooms two dimensional as the height never changes (although the player's height can change slightly), and maps are "boxy", with walls are rendered as textured, flat surfaces positioned at 90 (or, unlike Wolfenstein 3D, 45 degree) angles.
Floors and ceilings are not textured, but primitve skyboxes are introduced and if the player shoots a wall, the texture will change to a "damaged" variant, in effect creating primitive interactive scenery. Enemies are rendered as sprites, and, also impressive for Mega Drive standards, are scaled in real-time. Shooting enemies will also create "gibs" similar to more modern shooters.
The consequence of all this is that the 3D view is constrained to a small portion of the screen, with the rest being taken by the game's HUD. The frame rate and draw distances are also lower than in both Wolfenstein 3D and Doom.
Zero Tolerance and its unfinished sequel, Beyond Zero Tolerance, were released by the developers as freeware.