The Photowall app lets you alone or a group of Photowall users beam not just one photo, but an entire collage of images to your TV through the Chromecast HDMI streaming stick. The app also includes the ability to doodle or annotate images before beaming to a larger display.
Also, as noted by 9to5Mac, the app can automatically create a YouTube video for sharing the photo presentation in video form to anyone across the web making for a very simple (and cheap – Chromecast is only $35 and the Photowall app is free) social sharing solution.
It will be interesting to see how much Google promotes Photowall or enhances the product in the months to come as it doesn't seem to consider it a finished product. For now the company says "Photowall for Chromecast is a new Chrome Experiment that lets people collaborate with images on the TV – using phones or tablets."