To read books from Ebook Central at a computer (PC, Mac, Linux) you need Adobe Digital Editions.
To use Adobe Digital Editions with Linux you need to emulate it, for example with Wine.
How to download an ebook from Ebook Central to my computer?
You don't need as before (with Ebrary) to log in to your personal account to download an e-book, save bookmarks, make highlighting etc. Everything is connected to Umu-id and a personal account is not needed.
You can save bookmarks, make highlighting etc. both in the downloaded book (offline version) and in the online version, but the changes don't get saved between both versions. The savings are only connected to each of the versions.