For internal websites, Web Services sometimes relies exclusively on Bootstrap, without writing any additional CSS. This allows Web Services to create beautiful and intuitive interfaces at a fraction of time it used to. For custom, public-facing sites, Twitter Bootstrap helps save time on development with responsive grids, tables, forms, and other useful components.
If you implement a site with sites.uchicago.edu, it will automatically format for mobile display.
For mobile applications, front runners include JQuery Mobile and Sencha Touch. JQuery mobile provides a quick and easy way to equip your web applications with touch gestures. Sencha Touch provides a robust and sophisticated framework and requires some familiarity with object oriented programming.