Ju 288A

First seven prototypes with BMW engines

Ju 288B

Seven prototypes with slightly enlarged airframes and better defensive armament

Ju 288C

Final eight prototypes (of which only four were completed) with two Daimler-Benz DB 606 or 610 "power system" engines. This version was selected for serial production in 1944, but the programme was abandoned before this could take place.

Ju 288D

Mock-up of a Ju-288C with improved tail armament

Ju 288G

Design for an anti-ship version armed with a 355.6 mm (14 in) recoilless cannon

Sources:
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Brown, Eric, Captain - Wings of the Luftwaffe, 1979, Airlife Publishing Ltd., Shrewsbury
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Donald, David - The Complete Encyclopedia Of World Aircraft, 1997, Brown Packaging Books Ltd., London
Wikipedia - Junkers Ju 288