Bootstrap 4 Alpha 3 is the latest version of the popular Bootstrap framework. It features several changes from previous versions including moving from Less to Sass for styling, enhancing the grid system for better mobile support, dropping support for older browsers like IE8, introducing new card components, and improving tooltips and popovers with auto-placement. Some advantages are improved performance from Sass compilation and easier responsive design. Potential disadvantages include similar website layouts between sites and reduced need for web designers.