What's This File Type? tells you what a file is, and what program created it. All you have to do is right-click on the file, and select 'Bloody Hell! What's this File Type?' (other text available if you're sensitive).
If you have a file extension and you have no idea which application it is for, try this search. If we list the software itself we'll show it too.
Enter the file extension to find, with or without a leading period. e.g .doc, .fll, .rpp, .xml etc.
If more than one application matches, we'll show you a list.
Some further general hints...
If the extension has a number in it (e.g., .S25) and no entry comes up for that try again using the number "1" or "01" (e.g., .S01). Often such files are part of a series and only the lowest five or ten entries in the series will be in the database.
If the extension is all numbers and no entry comes up try again with .000. Again, often such files are part of a series.
If the extension ends with an underscore (_) and no entry comes up for the particular extension it's likely that the file is part of an install set and is a compressed version of a file with the same first two characters (e.g., an .EXE file in a compressed install set becomes .EX_).