startVal is an open source ultimate jQuery slider plugin. It's a lightweight, fast and customizable slider.
Siema is a lightweight carousel plugin with no dependencies and no styling. It is 100% open source - free to use on personal and commercial projects.
PulltoRefresh.js is a quick and powerful plugin for your pull-to-refresh needs in your webapp.
It has a plugin-based architecture, first-class support for resumable uploads according to the open standard: tus, and custom encoding backends, making it extensible and robust.
Quill is a modern rich text editor built for compatibility and extensibility. It's a free, open source WYSIWYG editor built for the modern web.
It's open-source (MIT), free and easy to use.
plotly.js ships with 20 chart types, including 3D charts, statistical graphs, and SVG maps.
Paper.js is an open source vector graphics scripting framework that runs on top of the HTML5 Canvas.
It offers a clean Scene Graph / Document Object Model and a lot of powerful functionality to create and work with vector graphics and bezier curves, all neatly wrapped up in a well designed, consistent and clean programming interface.
Chart.js is a simple, clean and engaging charts for designers and developers.
Tipue Search is a site search engine jQuery plugin. It's open source and responsive.
Tipue Search uses various modes for loading content. Static mode uses JSON, while Live mode grabs content from a list of pages. Tipue Image Search is a full image search plugin.
Leaflet is designed with simplicity, performance and usability in mind. It works efficiently across all major desktop and mobile platforms out of the box, taking advantage of HTML5 and CSS3 on modern browsers while still being accessible on older ones.
It can be extended with many plugins, has a easy to use and well-documented API and a simple, readable source code.