It supports Support epub, pdf, mobi, chm, cbr, cbz, umd, fb2, txt, html, rar, zip or OPDS
Its nicely customizable, takes up the whole screen when running including status area, has a night mode, can autorotate or pin the orientation.
Personally I really like using it plus calibre companion to sync files with my computer.
I copy-paste some sentence from a book into my note taking app, and search for that same text on my other device. Note-taking is easier to sync than reading positions themselves.
Calibre saves the reading position inside the metadata of the book, so you'd need a way to re-download the book every time you open it.
You can learn more at https://www.bookfusion.com/reading/cloud-library
PS: Founder of BookFusion
I have added this to the development roadmap and you will see it deployed by Q2 this year
We're working on both mobile support and web at the same time.
The cool thing is that the multi-device cloud sync support will also work with the web version.