Space Sketchr

App for Project Tango smartphones and tablets by Left Field Labs lets you draw in three dimensional space:

Space Sketchr is a playful demo app that demonstrates the potential of Project Tango technology by allowing the creation of virtual 3D drawings
in space using full-range motion tracking. Originally created as a
curious prototype to draw connections between two points within a given
space, Space Sketchr allows a user to create illustrations that have
virtual dimensions that you can walk around and view from any angle.
Imagine a new kind of sculpture or drawing with a timeline in space.

Whilst this app is available from the Android store, this won’t work on normal Android tech (it is expected that Project Tango devices will be available before the end of this year). This does, however, gives a taste of what these devices are capable of.

You can find out more about the app here