XCaliber Virtual Themes: XVT provides switchable WordPress themes support.

Dynamically change the website theme based on Virtual Host URL,
WordPress Page or Posting.

Share WordPress Plug-Ins with Virtual Side Bars and reduce the
overhead of costly installations.

A single WordPress native server instance can now support
Multiple Virtual Themes (MVT) and used in conjunction with
Web Server Virtual Hosting (VHost) is a welcome solution for
efficient use of resources and a reduction in overhead.

See the developer manual -> XCaliber Virtual Themes