Spacemapper

Spacemapper scans a drive or folder and draws every file and folder as a box. The size of a box matches the space it takes up, so large files and folders stand out right away. Folders contain their subfolders and files, and you can zoom in and out to look at any part in more detail.

It works like SpaceSniffer. Spacemapper only reads your files: it has no option to delete, move or rename them, so you can look around without risk. The only files it writes are its own settings and scan summaries (see Files Spacemapper writes).