Over 10 years ago game studio, Steel Minions worked on a proposed a third installment in the Zool series. It was to be called Zool Planets and never picked up.

No idea how many people here are familiar with Zool but it was an especially charming platformer for early PC gaming. I think it's more remembered on the consoles from the time but the best versions were on PC (Amiga CD32 for Zool 1, either Jaguar or CD32 for Zool 2, i gotta write a comparison of those).