OpenDocument (OD) and Office Open XML (OOXML, not to be confused with OpenOffice.org) are both standardized ISO/IEC file formats. They are both XML-based and were created for storing/exchanging word processing documents, spreadsheets, charts, and presentations. The availability of open standards is important to guarantee interoperability and avoid being locked into a monopoly, which can happen when using a proprietary format. Historically, this was the case when Microsoft Word Binary File Format was a very common file format. Anyone who wanted to use it was bound to purchase Microsoft software (until the format was reverse engineered).
OD has been a recognized ISO/IEC standard since 2006, version 1.1 is recognized since 2012, and version 1.2 has also been submitted to ISO/IEC. OOXML has been recognized by ISO/IEC since 2008, but there have been some controversies surrounding the introduction of the standard. As a first point, both formats serve the same purpose, OD has been there first, and OOXML is a lot more complex (the standard definition is over 6000 pages, compared to less than 1000 for OD). Richard Stallman has critized this and states furthermore:
Microsoft Office 2007 uses by default a format based on the patented OOXML format. […] The actual format is not entirely OOXML, and it is not entirely documented. Microsoft offers a gratis patent license for OOXML on terms which do not allow free implementations.
In addition to the criticism of the format itself, there have also been controversies about its recognition as a standard. Microsoft actively pushed the standardization process, and sometimes used questionable methods to get standardization committees to vote in their favor. This is reflected by the fact that there is an entire Wikipedia article on the standardization process and extensive coverage of OOXML by groklaw, a law blog concerned with software. There is a long list of complaints about the process which is too long to cover in detail, so let’s just look at one example.
OOXML Standardization in Sweden
A memo has leaked, in which Microsoft encourages partners to join the Swedish Institute of Standards (SIS) and vote in their favor, in exchange for “marketing contributions” and “additional support in the form of Microsoft resources”. The original Swedish wording is available here. According to SIS, at the time, this practice was not even against the rules. SIS first decided in favor of OOXML, but later declared the vote invalid. They claimed that this had nothing to do with Microsoft “buying” the votes, but was based on a technicality: one company had voted twice. This finally led to Sweden abstaining in the international ISO vote, since there was no time left to reach a formally correct decision before the deadline.
OD is recommended for all NATO members. In general, OD seems to be more widely adopted than OOXML. Looking at the situation in Switzerland, we can see that the Swiss eGovernment standard SAGA.ch in its version 6 recommends both OD and OOXML, without giving preference to any of the two.
A lot of applications offer support for both standards, e.g. LibreOffice, OpenOffice.org, Google Docs, Microsoft Office (support for OD added in version 2007 SP2). However, some applications may have features that are not part of the official standards (e.g. scripting is not included in OD), or not completely adhere to them, since they are both relativerly young.