Windows: If you'd like a simple and portable tool for sorting files via renaming and relocating them, MoveOut is a lightweight solution.
If you need a heavyweight computer janitor, you'll want to check out Lifehacker's own Belvedere. For lightweight tasks, especially when you're not on your own computer and need a portable solution, MoveOut renames and moves files based on simple rules.
Select a source directory and a destination directory — in the case of file renaming, you can pick the same for both — and then tell MoveOut if you want files that fit the variable you've set for that directory renamed, moved or both. MoveOut is freeware, portable and Windows only.