Is that available on GOG?

Not yet, sadly.

I know, I was just pointing out that lots of people don't even read the OP.

Total Annihilation?

Sorry, since we've moved to Starcraft almost immediately i thought that it'll do too.

Returning to topic, Constructor should be great too.

Q U A K E

Unreal.

Spectre VR - Except its not on GOG - but should be

I could imagine 1nsane being a blast to play.
Also Flatout is immensely entertaining in multiplayer at a LAN, I've had a few good races there.
Also I'd suggest Age of wonders 2 or Shadow Magic if you want turn based strategy.
Heroes 3 is a nice game, but I've tried to play it at a LAN which was a downright bore because we were 6 people each taking turns. Way too long between rounds, and the version I had was not happy with alt-tabbing out to do something else. Age of wonders allowes simultaneous turns. You still have to wait for the slower person, but when everyone takes their turn at the same time, the time you spend on your turn doesn't bore the others as they're busy spending their own time.