".epub" is the file extension of an XML format for reflowable digital books and publications. ".epub" is composed of three open standards, the Open Publication Structure (OPS), Open Packaging Format (OPF) and Open Container Format (OCF), produced by the IDPF. "EPUB" allows publishers to produce and send a single digital publication file through distribution and offers consumers interoperability between software/hardware for unencrypted reflowable digital books and other publications. The Open eBook Publication Structure or "OEB", originally produced in 1999, is the precursor to OPS.
openpub - Project Hosting on Google Code. an application of the Atom Syndication Format intended to enable content creators and distributors to distribute digital books via a simple catalog format. The mechanism through which compatible Reading Systems access the distributed catalog has three components: eBook content, XML catalog metadata, and an HTTP transport for the catalog. OPDS-compatible Reading Systems must support IDPF EPUB, and may optionally support additional formats.