Red Alert
As well as the link from this post's image it may also be helpful to see this page about how to play Red Alert without burning it onto a CD. Red Alert is a great old game, that was released as freeware to mark the release of Red Alert 3. I spent many days playing it when it was first released, and since rediscovering it I have spent many hours more. Compared to some of today's games standards the AI can seem quite stupid, but I think the range of units and buildings in this game still makes it one of my all time favourites.