FlipLink.me is a great option with many features, easy to use and incredible well documented.
Easy replacement of PDF, preview, cover, CMAMEs ....
Its chatbot agent, Alex, is delightful.

Clean dashboards for preparing and listing works, team features (still learning how it works), definitely to keep.
There's few things to polish:
Option to limit if either corporate mails only (domain) are accepted and hotmail/gmail etc..
Some additoon of Simple Color patet for backgrownd of docs or ebooks.
Maybe the login page needs some polish layout to ease open the resources.
But in general a cool option to manage e-books, flip or scrolling.