A legal/registered version of Half-Life II and an active Steam account are required
Jailbreak is a Half-Life 2 modification similar to Team Deathmatch for Half-Life 2, but with a difference: two teams, two jails. When you kill a member of the opposite team, they respawn, locked up inside your jail. When a member of your team is killed, they respawn inside the enemy jail. Your objective is to imprison every member of the enemy team. The twist is that you can break out members of your own team, by fighting your way to the enemy jail and opening the doors. The game goes back and forth until one team is entirely locked up, the losers executed (in a variety of customised ways), then the next round begins.