Deutschfavico.js (source code on GitHub) is an interesting and possibly quite useful library that makes it possible to show dynamic, animated content in your web app’s favicon.
While it allows you to display all sorts of visual next to the browser’s address bar – such as videos or even web cams live streams – the most useful use case favico.js lends itself to probably is displaying badges and notifications.
favico.js provides animations, colour customization and custom fonts for these badges. Check out the examples on the website to get an idea of what’s possible with favico.js.