Yup, what the subject says.
Personally, I'm a huge sucker for co-op, and I can't remember whether this is playable in co-op or not. Any insights?

No, not that I know about it. All you can do MP wise is start a bot match, or classic maps like in Unreal Tournament, Campaign in Co-Op is not possible...

It has no built-in coop, but there are several coop mods out there.I tried one some time ago.
As far as i remember, they didn't provide "full" coop, as in singleplayer just with more then one guy, instead it was more like multiplayer with the singleplayer maps. Had some bugs probably, too.
If you really want to coop Unreal, you could try it, but i wouldn't recommend it.
Rune, on the other hand, uses the Unreal Engine, too, and is fully playablein coop (with mod) and funny in "normal" multiplayer, too.
There are a lot of other coop games/mods out there, and also a lot of sites dedicated to it. Just make sure games are really coop, as for some coop = anything with more then one player, and not only when you can actually play a campaign with story etc.

If you have both Unreal 1 and Unreal Tournament ('99) you can play the unreal maps in coop mode by running them within Unreal Tournament with the OldSkool Amp'd mod. From the limited amount of time I've used it, it seems to work very well, and will automatically load all players into the next map when progressing (note that AFAIK, you must all be in the same map at the same time)
Check out the S3TC hi-res textures as well.
Get the DirectX8 renderer to avoid high framerate inducing weirdness, while still using S3TC, and not (I _think) mess up some of the skyboxes by using OpenGL.

Thanks for the information.

A friend made a co-op mutator for Unreal Gold.
I'll ask him if he still have it, and will post it here if some of you are interested, as I deleted my Unreal folder quite recently after having fucked it up with violent modding.

That's one reason why I've become so fond of Xbox 360 games, typically they do have co-op support.

That is indeed (sadly) true.

I am very much interested, thank you.
So I just bought Unreal Gold off GoG, and it DOES have Coop out-of-the-(virtual)box. You have to manually choose the level you want to coop on, much like on any other gamemode.
I still have to see whether it manages to jump to the next level automatically when one reaches the exit or not.

Well the little gametype he did (wtfcoop), was a co-op tweaked to handle annoying things, like weapons not respawning etc, making the game way boring when you play at 4 or more, because the maps aren't made for this.
I talked about it to him and he kind of... lost it as well. Sorry D:

(Well, look like somebody beat me to it, mentioning that there is a cooperative mode, so I'll just leave this post alone as a guide.)
Everybody saying there's no cooperative mode is confusing me -- I just finished a cooperative mode with a friend recently!
When creating a new multiplayer, there IS a cooperative mode you can use.
I'll start Unreal Gold and post the instruction in a few minutes.
In game, go to Start New Multiplayer, then under Select Game Type, pick Coop Mode, then start at map, "Vortex2" for the brand-new game.
There is some difference between the cooperative mode and the single player, though...
Weapons respawn at the pickup location indefinitely (Disappears when you pick it up, but comes back after a few seconds), but everything else will disappears permanently once a player pick it up. (Because of weapon staying, ammo shortage won't ever be a problem)
The game difficulty seems to be set to either medium or hard, don't think you can change this setting.
Once one of the player exit the level, other automatically exit the level with the player. Basically, no matter where everybody is, if ONE player got "LOADING" screen, everybody will too, they all advance to the next level.
The ending screen won't play properly (it's actually hilarious, take a look for yourself! Rocket launches with both of you still walking around... and the rocket just... hand there in the sky with both of you watching and waiting... and waiting...).

Here's a wiki page explaining how to run a co-op server on UT:
[url=http://wiki.unrealadmin.org/Running_a_co-op_server_(UT]http://wiki.unrealadmin.org/Running_a_co-op_server_(UT[/url])