Online textbooks ≠ a textbook online?

UPDATE: I think that I am going to use VoiceThread, maybe VoiceThreads embedded on a website. Also def. using PowToons and thinking about ThreeRing for uploading hard copies.

Dear all,
My Spanish 2 class is going to write an online, open-source textbook this year. That is going to be our year-long project. They're going to learn the grammar and vocab traditionally taught during S2 on their own because, really, they don't need me to learn that. They can find all of that stuff on Google, or ask one of their native-speaker friends (our school is 75% Hispanic). It is important to me that this be more than just a source of information but instead a place where students can discuss linguistic details, analyze sources, and engage with real material. I want it to be an online textbook that is not just a textbook that is online.

Here is my question to you: what platform do you suggest we use?

One person suggested iBooks Author. Don't get me wrong, it looks gorgeous. But I am unhappy with the fact that it requires an iPad, that you have to "publish" it (thus making it harder to perpetually improve), and that it is basically just a textbook, a movie and a notebook mashed together. I need more dialogue and sharing from our platform.

@SECottrell mentioned GoogleApps. Might be nice because our internal email is Google based.

@Petreepie shared her class' Simplebooklet on Chile. Although their book looks great, again I am left wondering how to make a more dynamic, conversation-focused text.

Here's a sweet wiki I've found on making online textbooks. Still working through all the links and I'll update soon.

Please help support our learners as they actively craft their digital footprint, engage in student-centered learning and gather real-life skills, and practice their Spanish!

Thanks!