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- Council of Wyrms
- Dark Sun
- Garweeze Wurld (Hackmaster)
- Forgotten Realms
- Kingdoms of Kalamar
- Mystara (aka the Known World)
- Wilderlands of High Fantasy
- Greyhawk Apocrypha – Unpublished and supplemental information from notable Greyhawk authors and editors.
- Greyhawk in the RPGnet Gaming Index.
- Living Greyhawk /RPGA page on the Wizards of the Coast site.
- Wesley Phillips' Greyhawk Page It has some sources of information about Greyhawk from AD&D edition.
- World of Greyhawk Board Play by post role-playing board set in the world of Greyhawk.
- d20 publishers and products
- Official website of the d20 System and the Open Gaming License
- Open Gaming Foundation
- The Hypertext d20 SRD – v3.5 d20 System Reference Document
- the d20 system wiki
- d20 System on the Open Directory Project
- d20 Resources - HTML reference documentation for d20 Open Content.