MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
App Store Inspiration - Best iOS App icons, screenshots, landing pages & heatmaps
App Icon Resizer - A service to resize your app icon to all needed resolutions
App Icon Template - Royalty free app icon creator for iOS, OS X and Android
App Icon Generator - Generate icons and images for mobile apps, android and iOS. No need to upload or download. Works on your browser
Bjango App Icon Templates - App icon templates for PS, Ai, Sketch and Affinity Designer