"In the spirit of the Humble Indie Bundle, we have decided to release the source code to Lugaru! Our community has already made some great mods by editing the levels and graphics, but source code access will allow for much deeper modifications."

by this David from Wolfire announces this pleasant news. They release the game under  the GPL2 but without game-data. They have included enough of the game data to run the demo version.

The Lugaru source code can be browsed online here, and you can use this command to grab it with Mercurial:

hg clone http://hg.icculus.org/icculus/lugaru