Web Resources Depot has released a free Admin Template for use in web apps. It’s a three-column design with a row of tabs, for navigation, along the top. With some modifications, it would work well for a web application, if you were developing one.
Personally, I would use the design during development, and swap it out with a unique theme when all the coding work is done. But if you’re trying to put together a web app, and you don’t have any design know-how, and don’t want to hire a designer, you could conceivably use this. I’d just recommend customizing it a bit, so it doesn’t look like you have the exact same template as someone else.