1
The idea came from a product manager I used to work with. He had a bunch of website comps that he needed to show some remote employees but didn't want to zip them up and email them out. Ideally he wanted to put them online somewhere and just send out a URL. Going to the URL would show the first image and clicking it would take you to the next. I put that together one weekend and it did exactly what he needed. He started creating new "decks" and sharing them on a daily basis.
I've since added the ability to attach a note to an image and for viewers to leave comments. You can come along and use the site completely anonymously to upload images and create a deck for sharing, but you can't edit it after the fact or keep multiple decks organized in any way. Additional pay features are inviting multiple users to your account so you can work together on decks, customizing the URL to your deck as well as the subdomain.
In the feature queue: CNAME your own domain to the site, ability to markup and draw on an image via <canvas> (almost complete), versioning, ability to lead a review with the presenter controlling the navigation and multiple users viewing, grouping and archiving of decks...the list goes on.
I see three groups as my primary audience: 1) product managers that need to share site comps or presentations to remote folks, 2) independent designers and 3) design firms, both of which need to share creative work with clients and collect feedback.