VerbalExpression lets you write regular expressions in English; Knwl.js is a natural language processor; 140medley is an entire framework in 821 bytes. Want a DOM selector engine other than sizzle? Try micro-selector, nut, zest, qwery, Sly, or Satisfy. Need a templating engine? Try T-Lite, Grips, gloomy, Transparency, dust, hogan.js, Tempo, Plates, Mold, shorttag, doT.js, t.js, Milk, or at least 10 others. Dates got you down? Check out Date-Utils, moment.js, datejs, an.hour.ago, time.js. Route with Pilot, filter images with CamanJS, write games in Crafty, or make a presentation with RevealJS or impress.js.
Of course, along with this prolific creativity in the JS universe comes some serious overload. A bit of natural selection will eventually get the best of these projects on your radar, but if you want to see the really exciting bits of evolution occurring you have to watch. Constantly.
Beyond the very manual process of adding a library, the site is also a chance for you to experiment with all sorts of tech and see in real time how it performs under a moderate load. Originally launched as a .NET application most of what you see today is running node.js under iisnode using Express w/ Jade templates (moving to doT.js as you read), a gulpjs build process, a homegrown CMS using AngularJS and VB.NET (gasp!), and a Lucene.NET search application in C#.