DOCX was introduced with Microsoft Word 2007, it's based on open XML and uses ZIP compression for smaller file sizes. The benefit of having open XML is that it is able to be read by applications, platforms and Internet Platforms. However to open it using any Microsoft Word that predated 2007 would require DOCX to be converted into a normal doc format.
DOCX improves file and data management and data recovery. DOCX extends what is possible with the binary files of earlier versions. Any application that supports XML can access and work with data in the new file format. The application does not need to be a Microsoft product it can be any application. Users can also use standard transformations to extract or repurpose the data. In addition, security concerns are drastically reduced because the information is stored in XML, which is essentially plain text. Thus, the data can pass through corporate firewalls without hindrance.
Microsoft Word 2007 Microsoft Word 2008 (MAC) OxygenOffice Professional (Linux) Word 2010
Open Office of which ODT is part of was developed by Sun Microsystems around twenty years ago. The software is open source and is seen as a viable free alternative to Microsoft's Office suite of products. Open Office opens most Microsoft document formats and is is provided as a free download, without restrictions on license. The writer application which produces ODT files is the word processing element of Open Office.
The Open Document Format is an open standard developed by Sun Microsystems under the guidance of OASIS (The Organization for the Advancement of Structured Information Standards). Originally the OpenDocument format was XML based and had at it's root, it now takes the form of a zip file much like Microsoft's DOCX format and takes advantage of the ZIP's compression technology to reduce the overall file size. Writer documents take the form of .odt and .fodt.
Microsoft Office 2007 Microsoft Office 2010 OpenOffice Writer