Osprey offers two free computer wallpapers.
In 1982, Beam Software and Melbourne House released the first computer game explicitly based on Tolkien’s work. You can play the old school Hobbit text adventure game online here.
CardBoard is an interesting project. It’s a bit of software that simulates a deck of cards in a digital playspace, and allows you to play with friends over a local area network. Keep an eye on this one, because remote playing via the internet is sure to come.
Dwarf Fortress is a free video game with two primary modes: Fortress mode, in which the player takes control of a group of dwarves and attempts to construct a successful and wealthy subterranean fortress in a mountain, and Adventurer mode, which places the player in the shoes of an adventurer as they wander the world and do battle with various creatures.
The game is implemented in text-graphics, and is donationware, so you can download and play for free, while the developers ask for donations to continue their work.
Retrospec has a selection of 8-bit games that have been updated for modern computers.