There are many ebook readers, several for every device.  But no one can synchronise my reading between the devices.  (i.e. none that I know of)

What I want is to read my book in bed on ebook reader hardware.  Then, while commuting, I pick up my phone and continue reading where I left off.  Back in my sofa at home I read on my tablet or TV.  Not to mention to be able to read at the computer.

I suggest skipping creating an app for every device but instead make it online.  I mean… what can’t be solved by HTML5 nowadays?

There is a solution, Ibisreader, which already today keeps some of my ebooks.  I can read my book at every web browser be it computer or phone.

What it lacks though is a better user interface and above all a better way to track where I am in the book.  It uses some kind of chapters? and they can span several screen heights.  I would like to have the browser know which page, screen wise – not paper page wise, I am on so it can open the right page when I continue reading on the next device.
There won’t be an exact match when moving from a bigger screen to a smaller, say a tablet to a phone, but unless I have a very big tablet with a very small font it won’t be far off; and probably not even then.

Ibisreader is F/OSS so I guess it would be a good place to start.  It could also be a nice way to learn Html5.