Both EPUB and ZIM are bundled standalone HTML. We have an ongoing Outreachy project to add ZIM support; adding EPUB support should be easier once that lands.

Wikisource is currently using the Wsexport tool to export its content in ePub: https://tools.wmflabs.org/wsexport/tool/book.php

Adding Ljonka because he wants to work on this topic during the upcoming Wikimania Hackathon.

After short meet up with scott (dev of ocg) i will try to imlement epub gen on top of https://www.npmjs.com/package/epub-gen and https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/Collection/OfflineContentGenerator/zim_renderer

waiting for new repo on gerrit to upload a working version, integration to collection should be easy, as tool call is equal to zim or latex/pdf renderer

In T97672#2407049, @Ljonka wrote:

waiting for new repo on gerrit to upload a working version, integration to collection should be easy, as tool call is equal to zim or latex/pdf renderer

Note this was done https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/Collection/OfflineContentGenerator/epub_renderer from here. :-)

You can find first working draft on this commit, it should work with NodeJs 5: https://gerrit.wikimedia.org/r/#/c/303348/1

On next step it would be nice to create a custom layout and design for mediawiki ebooks. To do so, we have to create some template files for nodejs module "epub-gen" which beeing used for ebook creating . As i am not a designer i would love to see some help from community here.

At Wikimédia France we have request from librarians to have this feature, useful for their public (ebooks on e-readers).

@Jules_WMFr For Wikisource there is http://tools.wmflabs.org/wsexport/ that does the job. But it does not works with Wikipedia

Yes, thanks :), but the request is for french Wikipedia articles.

while ocg will be replaced this module make no sense anymore.

In T97672#3122129, @Ljonka wrote:

while ocg will be replaced this module make no sense anymore.

...some more context regarding Electron vs OCG is also in T73660#3135402

A contributor added another request for this feature in giving feedback from the PDF functionality. Mentioning here for posterity.

As already announced in Tech News, OfflineContentGenerator (OCG) will not be used anymore after October 1st, 2017 on Wikimedia sites. OCG will be replaced by Electron. You can read more on mediawiki.org.