IconDrop is an open-source SVG icon-manager desktop app for Windows and OSX.
Essentially it comes filled with many ready-to-use icons packs to use in Photoshop, Illustrator or Sketch, for example, by simply drag'n'droping it (you are actually dragging a SVG file).
If you like Icon Drop, please, take a look at my other more powerfull tool called Design Arsenal.