*.o* (File Extensions starting with “o”)
[#extodt]: OpenDocument Text Format

See: Open Document Formats.

[#extout]: *.out

This could be any type of output file. One standard, known to have a file ending with “out”, is the “a.out” format (quite commonly using a filename of “a.out”).

File Formats (names starting with “O”)
[#opndocfm]: Open Document Format

Wikipedia's article for OpenDocument calls this “Open Document Format for Office Applications (ODF), also known as OpenDocument”.

Wikipedia's article for OpenDocument: section called “Application support” has a list of some software that supports the format. For instance, this is supported by:

  • LibreOffice and other derivatives of OpenOffice
    • This may often be the default file format for LibreOffice. (The actual default is customizable using Tools\Options...\“Load/Save”\General, in the “Default File Format and ODF Settings” section, “Always save as:”. The default value is “ODF Text Document”.) Nearby that setting, there is a setting to choose which version of ODF to use.
  • Microsoft Office XP (also known as Microsoft Office 2002) and Microsoft Office 2003, with third party add-on software (documented by MS KB 953331). At least some newer versions of Microsoft Office have support for this as well, including Office 2007 for Windows with Service Pack 2 (or 3) supporting “ODF 1.1”, and Office 2013 for Windows adding support for “ODF 1.2”.

There are several “Open Document” formats. These include:

OpenDocument Text Format (*.ODT) files
[#ofcwnodt]: (Old) Office for Windows ODF support

MS KB 953331: Description of Office Compatibility Pack Service Pack 2 says: “To open or edit OpenDocument format file types in pre-Office 2007 versions of Word, Excel, or PowerPoint, use the ODF Add-in for Microsoft Office. To download this add-in, visit the following SourceForge.net Web site:” “http://odf-converter.sourceforge.net/download.html#hDownloadOffice” “Microsoft provides third-party contact information to help you find technical support.”

Wikipedia's article for OpenDocument: section called “Application support” indicates that the “pre-Office 2007” versions that are supported are Office XP (also known as “Office 2002”) and “Office 2003”. (Speculated: Likely, earlier versions of Microsoft Office won't work with that add-on.)

Later, that same MS KB article 953331 notes, “Windows 7 adds the support in WordPad for the .docx odt.file types.” [sic]

Spreadsheet (*.ODS) files
Presentation (*.ODP) files