Many of us have experienced the annoyance of receiving a file that we don't have the appropriate software to view or in a format we do not know or recognize, e.g., "What is a .xxe file and how do I open it?"
(Disclaimer: Make sure you have up to date virus scan and check with the sender when receiving an unknown file. You have been warned.)
Many sites offer a list of file extensions describing the file type, but the one I like to use is Openwith.org because it also provides a link to the appropriate application for viewing or editing the file.
And in case you are curious, an XXE file is a Compressed ASCII Archive and can be opened with WinRAR.