Games

Interactive Fiction

Interactive Fiction is the new name for games previously known as text adventure games. The new games are mostly free and written by real writers instead of programmers. Some of my favorites, made by Adam Cadre : Photopia (Short, easy and has an excellent story. Good game to start), Shrapnel (Also short and almost puzzle-free. Violence and twisted humor) and Varicella (King has died and the ministers compete to become Regent. Palace Minister needs a cunning plan to eliminate the competition. Evil characters, treachery and dark humor. Relatively short, but has real puzzles).

Inform

Programming language(or "design system") for creating Interactive Fiction games.

The Interactive Fiction Archive

The archive itself.

Civilization clones

Freeciv

A very good clone of Civilization II (though has rules for Civilization I as well). Runs on both Windows and Linux (and several other platforms), has network play and, of course, is free.

Civ Evolution

Another non-commercial game based on Civilization. Features self-designable units and fully deterministic gameplay. Still in development, but reasonably playable already. The standard AI is pretty helpless yet, but there are others you can try.

Roguelikes

Dungeon Crawl

Perhaps not one of the most famous roguelikes, but one of my personal favorites. Simple, short and playable. Unfortunately, apparently no longer developed.

Nethack

Probably the most famous roguelike.

Angband

Angband is another popular rogulike. Has tons of variants.

Other

Areena-pelit (fi)

Gladiaattorimanagerointipeli.