Material Design for Bootstrap is a theme for Bootstrap 3 which let you use the new Google Material Design in your favourite front-end framework.
Read more about Material Design for Bootstrap visiting the Github page.
If you are looking for screen size data for a variety of devices, then look no further than screensiz.es. The size layouts common popular devices, including both mobile phones and tablets. It also includes popular desktops and high-end monitors.
A free and open sourced icon font. Brilliant for usage in your web projects, and can be combined with Twitter Bootstrap.