A plate reverb system uses an electromechanical transducer, similar to the driver in a loudspeaker, to create vibration in a large plate of sheet metal. A pickup captures the vibrations as they bounce across the plate, and the result is output as an audio signal. (wikipedia)It's quite similar in principle to shaking a piece of sheet metal to simulate thunder :) Plate reverbs have usually clean, bright, quite metallic sound and are suited (mostly) for vocal parts or percussion sounds.
Update: There is newer version - TAL Reverb III available.
TAL Reverb III in action by bjporter
Download: Togu Audio Line Reverb II / III