OpenDocument Format(ODF)

Now, ODF has been a ISO standard.

ISO/IEC 26300:2006 defines an XML schema for office applications and its semantics. The schema is suitable for office documents, including text documents, spreadsheets, charts and graphical documents like drawings or presentations, but is not restricted to these kinds of documents.

So, you can imagine that office documents will sooner or later be open in XML on the web. Openness and XML are absolutely the trends.
There have been some office applications online, there also exist some problems, such as lack of standard format, difficulty of dealing with binary content. ODF standard defines the schema, binary XML may be useful when encoding.

ODF specification was first proposed by OASIS.

OASIS (Organization for the Advancement of Structured Information Standards) is a not-for-profit, international consortium that drives the development, convergence, and adoption of e-business standards.