When we start google find the icon & icon editor, It will be show lots of online editor & some limited feature application only we can download it. But recently I have find best free icon editing tool from Syncfusion Product Metro Studio. You get more icons & easy to edit 6200 Icons template.Just login & download from this url.
This tool can you a good editing experience & You can export any types of picture or image format.
Even you can export like code format.
You can Generate Font Also-CSS
See this tutorial video