These links are either currently maintained and active, or useful static resources (although they may have been last maintained some time ago).

Game books

Both the main books are out of print, but watermarked pdfs can be obtained through DriveThruRPG.

Amber – the main Amber Diceless Gaming system
Shadow Knight

Amber Forums

Shadows of Amber – a great site for all your Amber needs!
Amber Forum at the RPG Site
Amber Diceless Role Playing – a not very active forum
The Amber Mailing List
Amber Discord server

Resources

Advantages of Amber: Diceless Gaming
Amber Diceless Notes
Maps of Amber – fan created
Amber Online – notes on the auction system and the geography of Amber
The Annotated Amber
Other AmberCons worldwide

Lords of Gossamer and Shadow – a variation on Amber

With further Amber publications stalled, a variant on the system was launched. You can read more about it here:

You Should Be Playing Lords of Gossamer and Shadow
Lords of Gossamer and Shadow – Rite Publishing