Ask HN: ePub reader with sync for iOS/Android and Linux

It can also be installed on Kindle, Kobo, Pocketbook.

EDIT: No iOS option sadly

I use BookFusion on iOS and Android, syncing everything with Calibre on Linux via the BookFusion Calibre plug-in.

Another vote for BookFusion, it is quite good

I can open source it if you'd like.

Google put a scary warning, which I can fix. But essentially it syncs via GDrive and will ask a permission to do so.

kindle app? amazon has read.amazon.com for the Lienix

Yes, but I want to avoid FAANG services