1. Chance.js Chance is a minimalist generator of random  strings, numbers, etc. to help reduce some monotony particularly while writing automated tests.
2. Lazyload images, iframes, widgets with a ~1kb standalone script. https://vvo.github.io/lazyload/
3. impress.js : https://bartaz.github.io/impress.js/#/bored : Awesome replacement of Powerpoint slides html css based slides
5. gnd.io : Ground :
Modern web application development framework
Create advanced web applications based on the latest technologies using a logical and light-weight framework. Built to provide seamless realtime client-server synchronization and complete offline support.
6. HTML5 SketchPad : canvas :
7. video call in browser : https://vmux.co/