E-reader web-based back-end?

[Ken D'Ambrosio]

Hey, all.  I'll admit it: I like to read.  And while my Kobo is awesome, 
sometimes, I have books I acquired outside of the Kobo ecosystem.  And 
it's annoying trying to read from one device to the other, and always 
having to find my page, copy files, etc.  Is there a web-based back-end 
for non-DRM'd ebook reading?  Shockingly (not), gooling "e-reader Linux" 
gets me lots of ways to read *from* Linux, but not to use Linux as a 
back-end.

Thanks for any pointers!

-Ken

P.S.  Looking for ebook, mobi and PDF support, if beggars have the 
option of being choosers.