BIG UPDATE
[new] Since 3.0.0, each of the visitors can set his own theme that won’t effect others’! We mean, there will be different themes for different visitors at the same time!
MDC Theme Switcher allows to choose and preview from available themes of a WordPress from front-end. Different themes for different visitors simultaneously!
Upon activation, it adds a sricky bar to front-end with a dropdown list of availabe themes. Admin can select which of the installed themes should be available in this list.
It also enables a shortcode [mdc_theme_swicher], that can be added anywhere of the WordPress. In a post, page or widget. Even in template files!
Video
Screenshots
Configure page
Sticky bar at bottom with dropdown list of themes
Sticky bar at top with dropdown list of themes
Widget shows dropdown list with shortcode