Apple App Analytics - Apple's very own iTunes Connect App Analytics
AppGrowthLab (by SplitMetrics) - 55 app growth lessons from 30 app marketing experts
Poltio - Create and share questions, get answers.
The Creative Marketer - Techniques & tools for copywriters, marketers, and creatives
My Motiff - Allowing you to stay connected in realtime
Adapty - Low-code price personalization for in-app subscriptions