website is not available anymore. lates facebook post in September 2016. latest commit on github in Feb 2018.
Discussion in this issue tells, that it was shut down, because they "didn't find it's place in the market"https://github.com/classeur/classeur/issues/242
I wrote a blog post about it on how to set this up for pushing classeur.io to wordpress here
In terms of things good about app.classeur.io
Its free up to 100 docs, $3/ month if you have more than that, $5/month if you want peace of mind with automatic backups to google drive
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