Blockate

Blockate is a sandbox building game where you can create worlds, or play them. In Blockate, you're able to create worlds and build in those worlds with blocks. You can use different shapes, colors, materials, and many things to build up your world. You can also have friends play your worlds, and even help build them.

Controls: 
Q - Toggle Spectator, Building, and Delete mode.
Shift + Q and Shift + E - Swap color
F and G - Change shape
Z and X - Change material
Alt - Copy block's properties
C - Toggle Main Menu
V - Toggle World Menu
Say !cmds for a list of commands.