Windows only: System cleaner application Clean Drive does only one thing, but handles it with ease — it searches for and deletes old files that you don't need anymore.
Once you've downloaded and launched the no-installation-required application, you can select a folder using the browse button — sadly you can't type in a path — and click the Scan Now button to search for old files, and the Delete Files button to get rid of them. You can't select individual files, so this tool would be best served as a quick way to clean out a folder on demand without deleting files that are too recent.
If you want more control over killing old files, you should check out how to use an advanced Explorer search to locate files older than a certain date, so you can easily move the files around if you need to. Clean Drive is a free download for Windows systems only.