Theme Switcher is a simple addon to that allows the user to switch between any theme at any time.

The block uses cookies to remember what theme the user has selected,

Demo

It also allows you to select theme via url with the theme handle:

http://alpha.mnkras.com/blog-page-type/?t=blue_masters

Where blue_masters is the theme handle.

Special thanks to c5studio who originally created this block,

and hereNT who helped out with implementing cookies and some other stuff.

If you can donate, thanks!