Torque (game engine)
The Tribes 2 engine, resold by former Dynamix developers for 100 dollars — one of the first game engines indie developers could actually afford.
When Dynamix was wound down, a group of its veterans including Jeff Tunnell founded GarageGames in 2000. They licensed the Tribes 2 engine and sold it as the Torque Game Engine, full source included, under an indie licence that cost a fraction of Unreal Engine or id's engines. Game logic was written in its own TorqueScript. Out came Marble Blast and a long tail of small-studio games through the 2000s.
Torque earned a reputation for being powerful but hard to tame — it was a real engine from a real game, quirks and all. Once Unity arrived with a friendlier editor, Torque lost ground. Torque 3D went MIT-licensed in 2012 and is maintained by its community.