Microsoft has made its Fluent System Icons open source, and now available for everyone to use. These system icons were originally designed for mobile apps, but perfectly suited as graphic elements for the Web. The icons come in both outline and filled styles, and have a friendly look-and-feel, with nice rounded edges and simple shapes, and do a really good job as functional visual metaphors.
Since the icon set is meant for developers, however, using them can get a bit technically involved. The Fluent Icons site does away with those technicalities, and makes the individual icons accessible to everyone.
Drop by the site and browse through the icons. You can search by keyword. Select an icon, and you can change its color, download it as a PNG, copy it to your clipboard, etc. It’s all very easy to figure out, tech wiz credentials not required! Here’s a very small sample of the icons in outline style (I prefer the filled versions myself):