The 1/2 AreaPlate is designed to 1/2 of a normal 96 wells surface area and volume for less reagents and other uses for smaller assays.
AlphaPlate is a microplate suitable for chemical emitting applications (especially AlphaLISA/AlphaScreen measurements).
The gray color is more suitable for assay on high density plates (especially 384/1536 wells) because the cross talk between wells is lower than white plates.