HTML/CSS Frameworks
An HTML/CSS framework reduces the boiler plate code that is required in a modern web application to implement features such as navigation bars, flexible column layouts and responsive design in general.
Bootstrap: Bootstrap is one of the most widespread HTML/CSS/JS frameworks given its emphasis on mobile-first, responsive layouts and its rich theme and plugin ecosystem.
Google Material Design Lite (MDL): Google Material Design Lite (MDL) is focused on implementing the Material Design principles in terms of user experience and look & feel. The emphasis here is arguably less on the responsive aspect compared to Bootstrap.
Foundation: Foundation is perceived as a more advanced and customisable framework than Bootstrap. It appeals to those who want to differentiate themselves from the ubiquitous number of Bootstrap-based sites.
Ernesto Garbarino