For some months now, it has been possible to use the Windows version of Universalis to create e-books that can be read on the Sony Reader, the Barnes & Noble Nook, the Amazon Kindle, and other devices. The Mac version can now do the same thing.
This web page will tell you all about Universalis e-books and how to create them.
Remember that if you have a mobile device such as Android, Blackberry, or Symbian, which can’t run any of the Universalis downloads, you may find that it is able to read Universalis e-books instead.