We all like old games. For what? For gameplay, originality, entertainment, maybe nostalgia. And those are the only weapons of free and old games alike against new, commercial ones. So I ask you: Do you have some favourite freeware games? (no abandonware, please)
My favourites:
1. Iji - for fantastic story, non-linear gameplay and RPG elements. I especially love possibility to play game in pacifist or slaughtering way, and many possibilities between those. Played trough several times.
2. Phobia 3 - thousands and thousands of aliens in every level, great soundtrack, cool co-op MOD, hours of fun. Everyone who likes to shoot things have to try this one!

Urban Terror, a fast-paced FPS built on the Q3 engine that has some great gameplay. Walljumping ftw !

These games weren't originally freeware, but they are now.
Ken's Labyrinth - The famous Ken Silverman Wolf3D mod where you try to save his dog. This game was a lot of fun when I was six.
Crime Fighter - I don't even know how to describe this game. But you must play it. I recommend the DOS version. :P
God of Thunder - A fantastic puzzle/adventure game with pretty graphics and good music.

[url=http://www.asahi-net.or.jp/~cs8k-cyu/windows/ttn_e.html]Titanion on Modern mode owns my soul.[/url]
You use some heat ray thing to make a big purple bug spew bullets at you, but then kill the bug and turn the bullets into one huge bonus.

at http://www.rockstargames.com/ click on downloads in the upper mid left of the screen. (it is a menu that only shows when the mouse is over it.) then click on rockstar classics and you can get Grand theft auto, Wild Metal and Grand theft auto 2 for free.

THAT'S what I call addictive gameplay :D And it has great graphics, too!
Ummm, it seems i should tell you what abandonware is: It means old commercial games for free download. We all know GTA, but good freeware game is hard to come by, so, please, no more abandonware in here...

OK I am sorry I just found out about it and thought that it was kind of a neat thing.

i am just posting in this thread so that I may look it up at home and try out some of the recommended free games on here.
also, perhaps padman???

Nexuiz.

Rockstar released them as freeware. It's not abandonware.

Nifflas' free exploration games. Astonishing ambiance, both through minimalism of the visuals and by the wonderfulness of it. Beats a lot of commercial games...
Plus it has a really retro look, hope you guys like it :)

Yeah, I played Knytt a few months ago and absolutely loved it, amazing atmosphere. Still need to play the other games :)
The Trilby games by Ben "Yahtzee" are great, good old style point n click games (scary as well) plus a pretty cool stealth one. http://www.fullyramblomatic.com/games.htm
Ben There, Dan That! is the most recent freeware game I've played (http://www.zombie-cow.com/?page_id=17) and it's absolutely hilarious.
http://playthisthing.com/ is an amazing site for finding nice little indie games, as well a weird and unique ones :)

Here's an article on top 5 RTS open source games you may want to try. It says Linux but they may have Windows versions too. I have Freespire Linux on another PC so I will probably trry all of these at some point.
http://www.junauza.com/2008/09/5-best-free-and-open-source-real-time.html

The Ur Quan Masters (Star Control II)
The source for SC2 was released a few years ago and a bunch of guys worked together to update the game and to get it to work on modern OSes while keeping the game the way everyone remembered it.
SC2 is a GOG, this version is free, and it's worth every penny.
http://sc2.sourceforge.net/

I've played it like 2 hours and it was really great :D But that's when I had to format. So no UQ anymore for me (as far as I could see it was really sucking my time).