RenderWare - powered a huge number of games over the years. Provided decent middle-ware to numerous developers. A shame EA got their grubby hands on it. It powered Grand Theft Auto III and it's many other PS2 era sequels.

Actually I have no great affinity with the engine, but it's one of those overlooked things when people talk about game engines.

Adventure Game writers on the old ZX Spectrum would no doubt say PAWS is the greatest engine of all time!