Active File is a little Symbian application that can make navigating around the files in your phone a lot easier.
It has two tab-like panels so you can actually view two places at the same time. This makes moving files between them, as well as folder comparison easy. You can also use Active File like a Windows TaskManager, as it will show you all active tasks, and allow you to kill any you think are unnecessary. Of course, you shouldn't kill processes unless you're sure you can!
Active File has excellent explore features, so you can look through saved messages, even create SMS message templates and save them where you want (instead of being told your phone is full, when it isn't). There is also a screenshot tool, which will save in JPEG, GIF, BMP, PNG, and MBM format.
Active File adds a lot of functions to your phone, but they will only be of use to people who really want to explore, and technical people who want to mess around! It's not the most intuitive application, even if it makes some processes easier (like searching memory).
Active File makes moving around the files on your Phone easier, but most users are unlikely to need it.