Today there’s certainly no shortage of icon sets and icon search engines (see the list below for a selection of those). These come in different flavours, mostly as icon fonts or SVG files, and can be easily integrated in a website or web application using standard HTML and CSS techniques.
A particularly ambitious offering though is the Noun Project. The Noun Project provides a huge collection of curated icons (or rather huge amount of icon collections) created by a large community. Their goal is no less than “Creating, Sharing and Celebrating the World’s Visual Language” and to “Help Build the World’s Visual Language“.
This focus on icons as a visual language rather than just a technical detail of an application shows. The Noun Project is largely technology-agnostic in that the site simply offers icons for download as PNG bitmap or SVG vector image files. So, there’s no emphasis on technical details such as how to use these icons in particular environments such as web applications. The Noun Project in a way is a return to what icons were in the beginning: A purely visual language for universally conveying meaning regardless of language.