IconStore - Free icon packs by first-class designers
Radix Icons - A crisp set of 15×15 icons. Open source.
Feather Icons - Simply beautiful open source icons
MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
Iconjar - Store all your icons in one place, just a click away
Ayecon - Ayecon is an app that allows you to easily make icons according to the required dimensions.