IPhone App or OS function to stop all apps
Since you mentioned GPS apps specifically, you can turn off Core Location ("Location Services") in the settings app.

Each app runs in it's own sandbox and is totally oblivious to other apps. There's no way with public APIs to know of other apps, so a "task killer" such as you might have on Android isn't possible on iOS.

Generally, a well-written app will not use excessive background resources. If you can find out which app is sucking resources, I'd recommend sending a support ticket into the developer and let them know what's going on. From my own personal experience as a developer, I'd love to know what I'm doing that makes my users upset, so this is win for both you and h(im|er).

The bottom line, though, is that you're stuck manually killing them. :(