The reader analytics firm JellyBooks has quietly launched a new cloud Reader app for the web browser. It is based on Readium 2, I am told, and supports English, German, and French, with Spanish coming soon.
Jelly Books' app builds on the work put into the NYPL's SimplyE app which launched in 2016, and if you would like to try it, here is the full-featured German version. Here's a public domain title in English which doesn't have all the features yet (just a matter of a few more weeks, I'm told).
JellyBooks offers what is essentially a focus-group service for publishers. It provides readers with free ebooks in exchange for collecting data about their reading habits. (This is the same data that Amazon, Kobo, and the other ebook platforms collect but do not share.)