Unity for Minecraft Beta 1.6.6 (The April Fools Update) is a release file of the Minecraft resource pack Unity. It was published on April 1, 2017 and is 0.3 MB in size. For the full description, screenshots and every other version, visit the Unity resource pack page.
How to install: Put the .zip into .minecraft/resourcepacks (do not extract it) and enable it under Options → Resource Packs.