App Ideas for WP & W8

So, you know how some people have all these ideas for apps but can't build them? I'm the opposite, I'm a developer in my day job, and I'd really like to build some apps for Windows Phone 8 & Windows 8, but can't think of a single idea as to what to build.

What sort of things do you want to do on your Windows Phone or your Windows RT device that you want to do but can't because there's no app for it? Obviously, I can't bring existing apps to the platform, but I can add my own +1 to the app count, and maybe make someone's device a little bit more enjoyable for them.

Post your ideas below, and I'll make mock-ups of the ideas I think sound interesting, update the post, and maybe start developing a couple of them.