Flat UI. Free Web User Interface Kit
Flat UI Elements PSD
The Flat UI HTML & CSS Kit is made on the basis of Twitter Bootstrap, a comfortable and functional framework that simplifies the development of websites. The framework has been proven over the years by developers from around the world.
Free awesome flat ui kit
Material Design - Style - Color-UI
Simple Line Icons Webfont
Need to start thinking of eLearning as more WEB than POWERPOINT. Love the use of grid layout here and the side nav - something to consider.
Flat UI Colors
Flat UI Pro is made on the basis of Twitter Bootstrap in a stunning flat-style, and the kit also includes a PSD version for designers. From $39. Learn More: http://designmodo.com/flat/