Upverter is a web service, similar to GitHub that allows you to discover, share and work on hardware.
Taking full advantage of HTML5, the included editor has all the basics you have come to expect such as undo, redo, rotating, versioning, and sharing designs. Create your schematics on an infinitely large canvas and organize your designs how you want to. Also included is their crowd-sourced part library to choose your parts, or add your own. Get insight into what parts are the most popular and cost efficient.
Here is an embeded drawing of Arduino-Uno:
You can connect parts and flags together with nets. The app will intelligently warn you when you are doing the impossible, or prompt you when your actions are ambiguous. Leave comments on your designs for you and collaborators to explain why certain decisions where made, or to remind you about sections you need to look over later.
Try it here: http://upverter.com