- MyDevice.io
- Device pixel density tests
- Viewportsizes
- What's my UserAgent?
- What's my browser?
- WhichBrowser - Which browser do I have and how does it identify itself? This site has an extensive database and an API.
- HTML5-Test
- Can I Use
- Tinytype - A compatibility table showing the available default system fonts across different mobile platforms.
- What CSS to prefix?
- haz.io - Which capabilities has your browser? Modernizr is used to check the browser's capabilities.