Just weeks after Frozenbyte did the "Humble Frozenbyte Bundle" which started on 12. April and had the prototype game "Jack Claw" with assets and source code for Windows inside today on the 23. May the source code for Linux and Mac showed up. This code is ported by Alternative Games (http://alternativegames.net/) just like the one for the Shadowgrounds series and for Trine.
You can find it here:
And also inside a mercurial repository here:
As "Jack Claw" and the Shadowgrounds series are using the same engine, Storm3D, it should be possible to hook the SG series on top of this code.