For the uninitiated, ODF is
an open XML-based document file format for saving and exchanging editable office documents (including memos, reports, and books), spreadsheets, charts, and presentations. OpenDocument was developed as an application-independent file format by OASIS (Organization for the Advancement of Structured Information Standards), a vendor-neutral standards organization.
ODF is currently employed by OpenOffice 2.0, KOffice, Abiword, and tons of other applications. Lots of other office suites and programs will likely follow. The recently formed ODF Alliance now has more than 150 member organizations.
(via Nico Golde)