The list has been updated with the following games:

Dungeon Keeper

• Dungeon Digger

Herzog Zwei

• Herzog 3D

Railroad Tycoon

• FreeRails
• FreeRails II
• Railz2

Total Annihilation

• Robotic War

Fleet Command, Harpoon

• Global Conflict Blue

Traaaainsssss!!!!!

Recently I've discovered a game called Subevel Zero, which is a 6DoF Descent-like corridor flyer/shooter with randomly generated levels. I checked if a playable demo was available, and found out that apparently this game was originally created for Ludum Dare, and a pre-release free/trial version is available from here.

The free version is quite different from the final commercial game, and it's somewhat closer to the original Descent as well. It allows for infinite play with randomly generated levels, and there are also random powerups that enhance the player's stats (e.g. increased rate of fire or maximum ammo capacity for a certain weapon). Here's a couple of gameplay videos:
Ludum dare entry gameplay
Commercial version gameplay

Freedoom v0.10 is out, with lots of improvements. More monsters and almost all weapons have been replaced with higher quality art. Maps have been updated as well.

Wyrmsun v1.8.0 adds the custom hero option and inventories for heroes and high-level units.

I haven't touched this in a long while, but recently I worked through the lists and completely rearranged them, based on more useful criteria. I also added a number of new games to the lists as well.