GitBook is a new-ish (2014) platform started primarily for writing technical documentation. Using Github versioning as the basis for writing-editing documents, the platform is growing very quickly. It is easy to see why, as it is easy to create well-formatted documents and publish them.
About 9 months ago, I started learning Arabic. The first challenge for English speakers is learning to read and write the Arabic script. I found the tactile experience of writing the script most helpful, not only learning to write, but for learning to read the script. I used GitBook to create templates to practice writing. Here is a link to the document at GitBook: Arabic Learning Templates
More to come on GitBook/Github no doubt.