Occasionally, especially in large corporate clients, I find myself looking at a file extension wondering “what sort of application created that?”.
Most often the file is intended to be a source of data for an SSIS extract & no-one can recall the legacy system that created it.
I found the following site to be brilliant.
FileInfo.com - The File Extensions Resource
The definitive resource for information about file extensions & file types.
Of course, it doesn’t actually solve the problem of getting a ODBC or other data provider to read the file. But at least it helps narrow down what might have been used to create it. Also helps the discussion when they’ve actually given you the wrong file.