Magnifique is an application that changes the themes of Mac OS X 10.5 Leopard at the flick of a switch. In just a few clicks, you can have a totally new look on your Mac.
Best of all, it's completely free but note that it doesn't come pre-installed with themes. You have to download them from the developer's site where you'll find 17 different ones to choose from. If you're a developer, Magnifique can also help you distribute your own themes. In fact, it's a perfect tool for developers that need to find a wider audience for their themes and work.
The interface is fairly self explanatory but the Add Theme button allows you to add themes to your library while the Remove Theme button deletes the selected theme from your themes directory. Make Theme is aimed at developers who want to create their own theme. Refreshing the theme list will add or remove any themes you added or removed while Magnifique is running. Finally, Restart Finder will allow you to see the effects of changing a theme although this is like killing the Finder process in activity manager which I don't like doing at the best of times. Restart Dock does exactly the same thing with the Dock.
Magnifique is an interesting tool although it should be used with care. If you apply a theme and it damages your default OS X theme there's little you can do so make sure you've backed up everything first.