Sets of just D6 dice - perfect for a range of wargames and RPGs that use 6-sided dice:

Year Zero Engine Games (Forbidden Lands, Coriolis, Alien, Mutant, Vaesen etc), Blades In The Dark, Judge Dredd, Open D6, Tunnels and Trolls (T&T), Fighting Fantasy, Wu-shu, Shadowrun, GURPS, Cyberpunk, Warhammer, Marvel Multiverse etc

D6 dice sets are also great for rolling characters in Dungeons & Dragons (dnd) and Pathfinder