De Gruyter has released its frontlist titles in the ePub3 format.
Here's an excerpt from the announcement:
The ePub format supports variable font sizes as well as the dynamic adjustment of content to the device's screen size. EBooks in the ePub format are released as a single file, as opposed to the one-file-per-chapter format of PDF-based eBooks. De Gruyter is one of the first academic presses worldwide to offer customers the choice between the ePub and PDF formats when purchasing an eBook.