Sophie

According to the site, Sophie is written in Java, but is used in Pier application MobileWikiServer.
Sophie is a FOSS collaborative multimedia "book" authoring system. Updates are instantaneous (no edit conflicts or merges) and multiple authors can collaborate on the same book simultaneously. (Educated guess: uses XMPP, ergo: Pier supports XMPP)

Note: From the Using Sophie Server video, it appears that Sophie Server is merely Pier, and that Sophie Author and Sophie Reader are Java apps.

Sophie Author allows users to create complex networked multimedia documents without specialized training.
Sophie Reader allows readers to read Sophie books in a browser without downloading a separate application.
Comment frames allow easily constructed spaces for discussion inside of books.
Browser frames allow embedding fully functional web browsers in book pages.
Sophie can import, embed, and export PDF files.
Easy to use embedded books: Sophie books can open inside other Sophie books.
Frame-based timelines present an easy way to create animations.
Sophie Server allows uploading, managing, and downloading books on a server.
Sophie Server allows simultaneous collaborative creation of books.

External links