It is the most popular project on GitHub and has been used by NASA and MSNBC among others.
Bootstrap was developed by Mark Otto and Jacob Thornton at Twitter as a framework to encourage consistency across internal tools. Before Bootstrap, various libraries were used for interface development, which led to inconsistencies and a high maintenance burden.
Bootstrap is simple to use. Look at few examples .
Bootstrap come with many ready to use features. See why to use at this link.