MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
Icons8 - Free app for Mac & Windows already containing 39,800 icons. Allows to search and import icons…
App Icon Resizer - A service to resize your app icon to all needed resolutions
Iconscout - Design Resource Marketplace.
App Icon Generator - Generate icons and images for mobile apps, android and iOS. No need to upload or download. Works on your browser
Craftwork - A collection of User Interface resources made by Craftwork