Open Microscopy Environment (OME)
OME is a multi-site collaborative effort among academic labs and a number of commercial entities that produces open tools to support data management for biological light microscopy. Designed to interact with existing commercial software, all OME formats and software is free, and all OME source code is available under GNU public "copyleft" licenses.
Part of it is the OME file format.
Project site: http://www.openmicroscopy.org/