In the Grimdark Future, There Is Only Biomass

Battle Primer (9th Ed. Core Rules) (PDF)

BattleScribe Army Builder

• 8th Edition Data File

Genestealer Cults Errata and FAQ (PDF)

Tactical Objectives and Stratagems

Tyranids Errata and FAQ (PDF, other factions available here)

Tyranids Hive Discord

Wahapedia

2d4chan:

• 9th Edition Rules
• Army Building and Playing the Game
• Genestealer Cults
• Movement 101
• Tyranids Tactics