D3
The D3...
Not much to say about it.
Warhammer 40k uses D3's every once in awhile - Rending, Manticores, & other cases such as +D3 attacks, 2 + D3 objectives, etc. Most of the time, they don't actually use a D3 - they just roll a d6, subtracting 3 from any result that's 4 or lower.