Radix Icons - A crisp set of 15×15 icons. Open source.
Smartmockups - Create stunning product mockups, easily and online.
MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
AppLaunchpad - Create free beautiful screenshots for App store/Google play
Ayecon - Ayecon is an app that allows you to easily make icons according to the required dimensions.
Placeit - Generate realistic product shots in seconds