Screensiz.es »

A table showing “the screen specifications of the most popular devices and monitors currently on the market.”

CodePen »

“CodePen is a playground for the front end side of the web. It’s all about inspiration, education, and sharing.”

“Need to build a reduced test case to demonstrate and figure out a bug? CodePen is great for that. Want to show off your latest creation and get feedback from your peers? CodePen is great for that. Want to find example of a particular design pattern for you project? CodePen is great for that.”

Stylesheet Download Tests »

This page tests “whether today’s browsers will download stylesheets that are referenced with media queries that would not apply on that browser or device.”

Thee appears to be a lot of download overhead with media queries using link elements.

Pears »

“Collect, test, and experiment with interface pattern pairings of CSS & HTML. Pears is an open source WordPress theme, enabling people like you to get your own pattern library up and running quickly.”