Lubith is a service aimed at people who want to create their own customized WordPress theme, rather than use a premade one. What's nice about Lubith is that it doesn't require any sort of coding skills or CSS knowledge; all you need to do is drag and drop things, pick colors, set a few fonts if you like, and you're done--Lubith generates a valid WordPress theme for your website. It's available in a free version and in an $87 one-year subscription.
Unfortunately, I can't say Lubith is powerful. Even if you utilize its full power, dragging things all over the canvas and changing colors with abandon, you are still going to end up with something that looks fairly generic. It allows for roughly the same level of customization you can get with highly customizable free theme WP Paintbrush--and just like WP Paintbrush, it is eclipsed in features by Artisteer, a downloadable program for creating themes for a number of content management systems.
Lubith makes it easy to change the layout of your blog and the location of the various elements on the page: To move the sidebar somewhere, just click and drag it. To resize it, click and drag its corner, which is highlighted with an unmistakable, easy-to-click orb. Some elements you can even eliminate; not all, though (the free version won't let you do away with the sidebar). Lubith doesn't let you apply entire color schemes in one fell swoop, nor does it support special fonts (other than the stock browser fonts such as Arial, Tahoma, and so on), and it includes just one default look to get you started. However, even the free version is blissfully free of ads and other annoyances, so you can just focus on the look you're trying to create.
If you think you'll be coming back to Lubith in the future, you might want to pony up for a one-year subscription (currently $87). A paid subscription saves any themes you created with Lubith on the server for as long as the subscription is valid. Of course, even when using the free version, you can simply export the theme you're creating and continue working on it outside of Lubith using other tools.
There's no denying it: Any blog you create using Lubith will end up looking like a fairly standard WordPress blog. Still, if you are just looking for a basic way to customize a WordPress installation, Lubith is free, easy to use, and very fast.