Basically you write your presentation in markdown right in the page, and you get an html5 presentation that looks like a ppt but is better. You can edit it has many times as you want.
If you save the presentation while you are authenticated (only facebook for now), you can share the link to view the presentation but no one can edit it except you.
The code is opensource and it is here. Any feedback is welcome, don't hesitate to send me a pull request and I will push to the heroku app.