What is Trouble in Terrorist Town?
Trouble in Terrorist Town (TTT) is a gamemode included with Garry's Mod. The game is about a group of "terrorists" who have traitors among them, out to kill everyone who's not a traitor.

A small number of players is selected as Traitors, who have to kill all the Innocent players (ie. the rest of the players). Those innocents know they are in the majority, but they do not know who is Traitor and who is not.

The Traitors must use the element of surprise and their special equipment, if they are to succeed. The Innocent just have to survive, which means finding out who the Traitors are and killing them before they kill you. Of course everyone is holding a big gun, and everyone looks suspicious...

For the Innocent, knowledge is power: who is acting strangely? Who can be linked to evidence found on corpses? Who is still alive, even?

What does it look like?
The best way to see it in action (besides playing it) is watching a videos. What happens in a round depends on the people you play with and the server you play on (many have unique weapons and additions). If you prefer pictures, there are a few in this old screenshot gallery. They're rather old at thjis point, so imagine it's all a little prettier than what you see there.

How do I play?
Follow/check these steps:
  1. You need to have Garry's Mod (GMod) installed on Steam.
  2. You need Counter-Strike: Source installed.
  3. In GMod, join a TTT server.
Where do I get it?
As mentioned above, you do not need to manually download or install anything besides GMod and CS:S if you just want to play.

If you are a server owner looking to host a TTT server, or a mapper making a TTT map, you probably also don't need to install anything, because TTT comes with GMod.