Bootstrap is a free collection of tools that makes up a front-end framework for creating web applications.  It focuses on the graphical components of a web application and contains HTML and CSS-based design templates for fonts, forms, buttons and navigation.  The goal is to encourage consistency and improve maintenance across internal tools.  Since version 2.0, Bootstrap supports responsive design, allowing the layout of a web page to adjust dynamically given the size of the screen on the device being used.