Font Awesome

Dave Gandy released it in 2012, originally as a companion to Bootstrap, and the trick was elegant: put each icon in a webfont as a glyph and it inherits font-size, color and text-shadow for free, stays crisp on retina displays and costs no extra image request. At a time when SVG support was patchy, that solved a real problem.

The downsides showed up later: icon fonts squat in Unicode's private use area, misbehave for screen readers, and block rendering until the font loads. Version 5 (2017) therefore added an SVG-based variant and split the library into free and paid tiers. Most new projects reach for inline SVG or a component library instead, but the fa- class prefix persists in an improbable number of codebases.