They've been developing the Liquid Textbook platform for a couple of years now, and this week they announced that they were updating the reading app to HTML5. The new app will be browser based, like the current Flash based app. Symtext are promising full cross-platform support as well as active content sharing. If a student adds a note from an Android tablet that note will be visible from the student's laptop almost immediately (so long as it's logged in to the same account).
It also has full support for selling the custom textbooks, and if a teacher puts serious work into developing their own textbook they will have the option of selling it through Symtext and reaping some reward for their effort.
The Liquid Textbook platform supports both private and shared notes, and the public notes are limited to just the class that the student is in. This makes LT a couples steps better than Kobo or Kindle, both of whom simply have a (completely) public sharing option. Students can also highlight notes as well as print the textbook.
Check out this demo video for more info:
Sharing could be the key here. While I'm too private of a reader to use the option, I did notice at the WirelessEdTech conference last week (here, here) how much teachers wanted more sharing options and how it affected their student's ability to learn.
The new app will go into beta test in January, and hopefully expand to include all users by the end of the year.