EPUB is a e-book file format that is gaining popularity and is supported by most e-book readers and software tools. BISG (a U.S. organization for industry standards and research related to books and publications) along with the release of EPUB version 3 announced, that the industry should endorse EPUB as the industry standard for digital publications.
EPUB format standard was developed by IDFP (International Digital Publishing Forum), a standard association for digital publishing industry. IDFP has been some time later acquired by W3C. The format is still actively developed.