Divshot is a rapid UI development tool built onTwitter Bootstrap and integrated with Bootswatch. Drag and drop interface elements and edit on the fly. It outputs clean HTML and CSS that is already responsive.
Web Lab, a collection of web-powered experiments created by the folks at Google, puts Chrome and the modern technologoes it supports to the test. Create music on real intruments with people around the world, or make a drawing and watch robots draft your creation in real-time. The physical and digital world unite in these mind blowing experiments.
Ever take a screenshot on an iPhone then have to email it to yourself, open Photoshop, and paste it into an image of an iPhone? It's a pain in the neck. Now you can just email that screenshot email@example.com and this free service will email you back with your screenshot composited into an image of the device it was taken on-iPhone, Android, iPad, etc.