RTF

RTF (Rich Text Format) is a format for word-processor-type documents created by Microsoft and intended to be more broadly portable than their application/version/platform-specific file formats such as DOC and DOCX, but still proprietary to Microsoft (though other vendors' software can also read and write it).

Specs

 * RTF 1.0 spec
 * RTF 1.5 spec
 * RTF 1.6 spec
 * RTF 1.8 spec
 * RTF 1.9.1 spec
 * Some other spec versions in various formats including RTF itself

Software

 * LibreOffice
 * Microsoft WordPad

Sample files

 * Sample document saved from Windows Word 2007
 * https://telparia.com/fileFormatSamples/document/rtf/

Other Links

 * Wikipedia article
 * , from the Encyclopedia of Graphics File Formats