See Greenhouse.

Revised Action Space rules:

• Creatures and assistants are assigned to action spaces as attackers are declared. "Declare attackers" step could be renamed "declare assignments," with creatures being assigned either to attack or to activate an action space. Both choices cause the creature to become tapped. • Creatures are removed from action spaces as permanents untap during the untap step. • "Assistant," if they exist, are game objects that can use action spaces. I've considered making it possible for planeswalkers to be assigned to them as well.

I made this a Construction because flavorfully it doesn't make sense as an enchantment to me, but mechanically it could be an enchantment or an artifact or a land.

Hey, I recall that idea from my own cards: Gaea's Garden. It's the same basic principle except I care for the power of the working creature(s) rather than have only a single slot.

So mine's more like crew.