Update: Bill McCoy has reminded me that there is an existing spreadsheet that shows which ebook platform supports which Epub3 feature. It's maintained by the BISG and can be found here.
I may have missed a name or two, so feel free to mention them in the comments.
This 4 year old company has long since pivoted away from publishing enhanced ebooks and is now a production and distribution service. Vook currently distributes ebooks to all the major ebookstores, but their Epub3 distribution is limited to iBooks, Samsung Reader Hub, and Sony Reader Store. Vook also supports the Kindle Store, though it is not clear just how many features are supported.
Like Vook, Aquafadas is an ebook production and distribution service. I don't think I was able to get a complete list of where they can distribute Epub3 but I was told that the list includes iBooks and the Kindle Store (more on this later).
This service boasts of making an Epub3 picture book for KF8 and iBooks. It also lets you make Epub and other formats but does not support distribution.
This is a relatively new distributor that launched back in January, They can take an InDesign file and convert it to a fixed layout Epub3 which can be sold in iBooks, the Kindle Store, and (coming soon) the Sony Reader Store.
I don't have as much info on this company as on the others, but I do know that it offers an InDesign to fixed layout Epub3 conversion service. They boast that their output will work in iBooks, and the Kindle Store.
This textbook distributor supports Epub3 in their own platform and offers their own ebook creation tool, Inkling Habitat. It's not completely clear whether your Epub3 ebook will be sold as Epub3 or as Inkling's own Epub3-ish format. I'm not sure it matters, though.
1. If you're wondering why the Kindle Store is mentioned in a post about Epub3, it's because that's how several of the services talked about KF8 and Epub3. The formats are not exactly interchangeable but apparently the conversion services feel that if you produce one you might as well produce the other.
2. The complete list of ebookstores that I can confirm as selling Epub3 include:
- Gumroad (a marketplace, not an ebookstore, but you can sell your own EPub3 here)
- Kindle Store (Amazon supports conversion from Epub3 to KF8 - check out KindleGen support docs for more info)
3. Naturally this info is only as complete as my current knowledge, so I would deeply appreciate any help in expanding this list.