3D Place is a /r/place but in 3D. Every voxel you place is broadcast to a central server and persisted to disk. Come back tomorrow and your build is still there, along with whatever other players have added in the meantime.

You can place one voxel every 2 seconds.
The map size is 512x512x128.

Controls :
Left click | Place voxel of selected color
Right click | Remove voxel
Sroll Wheel | Change color
Middle click | Eye-drop color from a voxel
Tab | Gives you control of cursor so you can pick a color. Press Tab again to move camera around.
C | Toggle first / third person
T | Open chat
R | Respawn at world center
V (hold) | Voice chat (push-to-talk)
F | Fly
Shift (hold) | Sprint
Ctrl (hold) | Crouch
Space | Jump