I had to learn more before I throw out PowerPoint, so I Googled (which is difficult because of the top level domain in the name, had to search with quotations). http://ltlatnd.wordpress.com/2013/05/20/slid-es-for-lightwei...

TLDNR: Formerly Rvl.io, free tier, commenting. Paid tier at $7/mo has revision history, private slides and offline export.

And no, I don't work or know Hakim :)