One of the most popular DOS computer games in the good old days was "Scorched Earth" - sometimes called "The Mother Of All Games". I can't believe that I spent hours playing this game, my tank trying to blow up other tanks.
They now have Scorched3D, which is based on the classic DOS game.
They now have a 3D island environment and you can even play with other opponents over the net- it has LAN and multiplayer support. The latest version 40.1 has dynamic lighting, tank tracks and other enhancements including 50 total weapons to choose from.
Amazingly, Scorched 3D is totally free and is available for Microsoft Windows, Unix, Linux and Mac operating systems.
Just one thing though, you will need an XP PC with at least 512MB memory and 128MB video card in order for the game to run nicely.