Sonic Souls, by Doky
1.8 (2014)
Download | Webpage
Sonic Souls got updated with graphics improvements and other changes.
Forgotten Paradise, by Zeduardo35
Unreleased (2014)
Video
A new level from the same author of the Iron Cave level.
And from Zeduardo35 too, a little video collection about the creation of a SonicGDK level:
VIDEO 1 | VIDEO 2 | VIDEO 3
VIDEO 1 | VIDEO 2 | VIDEO 3