Loving this One Pager for the (free) Overgram iPhone app. It has such a good demo, you just have to sit and watch the iPhone whilst the browser background also previews examples. Brilliant.
This website has unfortunately been redesigned or gone offline, so I have removed the direct link to it. The screenshot below hopefully preserved enough of the design but if you are really keen to inspect further, try this Archive.org link. FYI: the site was first featured on 18 November 2012.