Mojang is currently testing mini-games in Minecraft.
As detailed in the video below, the current beta build for the subscription Minecraft Realms service offers mini-games as a selectable option from the main menu.
The current offering includes Cake Defence 2, Blocks vs Zombies, The Walls, Autospleef and Dash of Doom. All player worlds return to their previous state when the mini-games are exited.
All games will be included in Realms’ 1.7.5 update.
Here’s the video: