This post will be continuously updated/revised.
Charts and graphs: https://gionkunz.github.io/chartist-js/
Charts and graphs: http://www.chartjs.org/
Sortable tables: http://tablesorter.com/docs/
Vertical slides: http://alvarotrigo.com/pagePiling/#page1
tablecloth.js is a jQuery plugin that helps you easily style HTML tables along with some simple customizations.
List.js adds search, sort, filters and flexibility to plain HTML lists, tables, or anything.
Select 2 is a jQuery based replacement for select boxes. It supports searching, remote data sets, and infinite scrolling of results.
scrollMonitor allows you to receive events when elements enter or exit a viewport.
ScrollReveal - Easy scroll animations for web and mobile browsers.
Emmet Re:View - A browser extension for displaying responsive web-pages in a side-by-side views to quickly test how it looks at different resolutions and devices.
MailTrap - Safe email testing for dev teams.
Learn Layout teaches the CSS fundamentals that are used in any website’s layout.
The Voca library offers helpful functions to make string manipulations comfortable
W3.CSS is a modern CSS framework with built-in responsiveness. It's based on Google's material design, and is extremely light and easy to work with.