Fela is a fast and modular library to handle styling in JavaScript. It is dynamic by design and renders your styles depending on your application state.: https://github.com/rofrischmann/fela
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: http://re-view.emmet.io/
Underscore is a JavaScript library that provides a whole mess of useful functional programming helpers without extending any built-in objects: http://underscorejs.org
A modular, front end framework to easily and quickly help you jumpstart your process in building complex interfaces for the web right out the box: http://danmalarkey.github.io/schema/index.html
Lightning fast, super simple web framework written in Crystal: http://kemalcr.com
Amber is a web application framework written in Crystal inspired by Kemal, Rails, Phoenix and other popular application frameworks: http://www.amberframework.org