Open Dune 2

Dune 2 is a Westwood Studios game put together back in 1992, and it's probably best known for being the prototypical RTS, one of the first games to put together all of the elements that later led to the genre that made StarCraft and Command & Conquer so popular. 

This version is authentic. It's a nice trip down memory lane, or maybe just a free introduction to a piece of PC gaming history.