Anima App - Design, get feedback, convert to code, publish, iterate.
MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
Sketch Repo - Collection of resources for anyone who uses Sketch
EasyAppIcon - EasyAppIcon helps you to create your own app icons easily. Supporting Android Adaptive Icon!
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
App Icon Maker - Create icons for mobile app stores online for free.