2+
The gates come in 7 sizes (5×3 4×3 4×2 3×2 3×1 2×2 2×1). They open and close with E like any other door and place towards you (unless you rotate).
This is a modlet and does not require a world restart. Simply place into Mods folder and play!
Tested and works with Alpha 19.2 b3
Recommended to be played single player or multiplayer. Works fine on servers as well.
Changelog
Added a 2×2 size variation.
The forum topic of the mod is here.
Credits: Telric
2+
Very nice looking, but actually useless, because 500 HP thru that are zombies in no time…