The theme switcher plugin allows your readers to switch between your installed WordPress 1.3 themes. This switcher is based upon Alex King’s style switcher but has been adapted to switch WP 1.3 themes instead. It is very similar in operation to the style switcher. After activating the plugin, you add a call to
wp_theme_switcher() to your templates. This will present a list of all installed themes from which the user can pick and choose. Selecting a theme sets a cookie, thus persisting the user’s theme choice. If the selected theme is ever deleted, WordPress falls back to the default theme as specified in the admin area.
The first 0.1 release of the plugin is available here. As the 0.1 version suggests, this plugin is a baby and very well may be a bit colicky.