Documentation

API Reference
Comprehensive API reference documentation for GtkD libraries.
Wiki
The public wiki is located on the github project page. It's content is still very limited, but anyone can quickly contribute interesting links or knowledge there.

Tutorials

gtkDcoding
An ongoing blog series by Ron Tarrant with numerous small tutorials on various gtkD subjects.
GExperts
Blog posts about GtkD by Gerald Nunn made while developing the successful Tilix terminal emulator.