Many of these link directly to files at Happy Puppy, where you can find loads of games.

CyberDogs and C-Dogs Free DOS games made by Ronny Wester. Multiplayable wonton destruction.
Escape Velocity Shareware for Macintosh; published by Ambrosia Software. Blow up stuff in space. Essentially limitless customizability with plug-ins
Scorched Earth This version, 1.5, adds photographic textures and other cool stuff to "the mother of all games."
Worms Demo of Worms, the original classic.
Sim City Maxis' highly addictive urban planning (and demolition) classic (links to the newer 2000 version.)
Dune 2 Published by Westwood Studios, Dune 2 was the first RTS game. Based on Frank Herbert's excellent series of novels.
Terminal Velocity DOS shareware. This simple 3D flying game is one of the many excellent games made by 3D Realms. Check out some of their other game demos on their download page (such as Duke Nukem).
Ascendancy The first game published by The Logic Factory, this is the demo of a fun turn-based strategy game.
Syndicate and Syndicate Wars Published by Bullfrog, these successive games employ an isometric engine for team combat.
UFO: Enemy Unknown (A.K.A. X-COM: UFO Defense) Published by MicroProse (originally by Mythos Games). Operate the international Extraterrestrial Combat Unit and save the planet from alien invasion.
Planet Quake Home of Quake information, such as the Quake Developers page.
GameSpot Reliable demo downloads and reviews.

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