I personally wrote the code behind Sandstorm's "appdemo" feature, which is what the "Try it now" button links to, from the Etherpad front page. Etherpad itself is not written by me; it's written by many other great people.
One other possibly-cool thing is that any open source web app, when packaged for Sandstorm, can get a "Try it now" button of your own. That's what I explain at https://blog.sandstorm.io/news/2015-02-06-app-demo.html but I figure it's worth stating clearly here in a comment, to save people a click.
I personally wrote the code behind Sandstorm's "appdemo" feature, which is what the "Try it now" button links to, from the Etherpad front page. Etherpad itself is not written by me; it's written by many other great people.
See e.g. https://github.com/sandstorm-io/sandstorm/commits?author=pau...
I also wrote this blog post about the feature: https://blog.sandstorm.io/news/2015-02-06-app-demo.html
Happy to answer other questions if you have them!