Google And Lego Collaborate And Announced 'Build With Chrome' Construction App
The story goes as such: a Google team in Australia developed this in 2012, and just now it's being opened up to the world. The social aspects are (naturally) powered by Google+, but you can ignore all of that if you're just keen on building. As of now, the brick selection isn't incredibly vast, but it's a great time waster for those who love LEGO blocks.
The web app should work on Android as well as Chrome for Web, and you should have luck in Firefox as well. (Sorry, no IE 11 support!) Enough chatting -- head on over and start building.