An extra 2 players, Digmo (green) & Jane (pink) were recently included in the July build which is available for download.

Four players
Recently added 4 players

Currently, they can be used in multiplayer games or locally with 4 controllers.
We're working on adding support for a combination of keyboard (limited to 2 players) and game controllers.

Tester Rick (fellow Australian) has made a starter pack of 5 puzzles that you can play. So grab some friends and give it a go!