Animations & sprites

Special effects recipes (including animations)
      rive package
      Spriter Pro tool
      spriteWidget package

App review

app_review package

Audio

audioplayers package

Firebase

Flutter Firebase getting started guide NEWLY UPDATED
      firebase_crashlytics
      package (tracks crashes of your app)

Game engines

Flame engine
      Bonfire engine
      forge2d package

Games services

games_services package

Images and icons

CraftPix (free and purchasable assets)
      Game Developer Studio (purchasable asset packs)
      GIMP (a free image editor to create your own assets)

Persistence

shared_preferences package
      sqflite package
      Couchbase Lite, cbl_flutter package