The Noun Project has started a project to share free icons to the world. It comprises many of the highly recognizable set of everyday icons. They are all on creative commons license which enables you to share and edit the icons to your liking. You can also use them for commercial purpose.
As the name of the site, the icons are to listed in well know categories then grouped together with the noun they represent. There isn’t any search option currently on the site so you have to browse through the site to find icons that you may like. Or you can simply change the url of the page to see if icons exist with that noun.
The format of categories are in. So you can change the last part to find something you need.
The files downloaded are in SVG(Scalable Vector Graphics) format so you are going to need a software that is able to edit .svg formats. And thats where open source InkScape comes handy. Its a alternative for Adobe Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
Now that you’ve got the tools and a open source software that you can use to edit these icons. You can go ahead and grab a few icons for your projects on application, web or just designs.