Smashwords is the most likely.
It is primarily a distribution service for Indie publishers (hence the new, and lesser known authors) but it also operates an ebookstore that is very easy to forget exists. With cause:
https://www.smashwords.com/
Their titles can be found at Overdrive, Kobo, Nook, Apple, and a few other epub-based ebookstores, occasionally mislabeling Smashwords as the publisher.