Adapty - Low-code price personalization for in-app subscriptions
Really Good Emails - A large collection of good product email design.
Apple App Analytics - Apple's very own iTunes Connect App Analytics
Good Sales Emails - Best sales emails from great companies
CleverTap - CleverTap offers blazing fast analytics, powerful real-time segmentation, multi-channel messaging, A/B testing and personalization in one unified solution.
Great Email Copy - A dose of emails from around the web.