Windows only: While Windows Explorer can sort files by type, by default it doesn't display or sort files by extension in a separate column—but the Extension Column add-on does just that. Install this small utility to add a column to Explorer's Details view that lists the file extension (TXT) versus the default file type (Text document). A tiny but useful thing. Here are some more useful free Explorer add-ons. The Extension Column is a free download for Windows only.