OpenRA

OpenRA is free realtime strategy game similar to 'Command & Conquer' and 'Command & Conquer: Red Alert'. The game has a mod for Dune 2000.

You can choose between three game mod-s: C & C, C & C Red Alert and Dune 2000.
The game can be played in network or offline, you can add computer players (bots). There are various bots with varying difficulty, but all do extremely well. There are no stupid bots here and this makes the game quite challenging.

Installation is easy - download and run the installer, and it will download and install everything you need. When you play the game in some of the 3 mod-s for the first time, an mod package will be downloades, so you will need internet connection. If you need to be sure that you can play onffline, just run every mode once, to download all the files.