Google has created a browser-based block programming language: blockly – A visual programming editor – Google Project Hosting.
The editor is clearly inspired by Scratch, both visually and in terms of the programming features they chose to implement:
I found the blockly editor very irritating to use (no cut and paste, every block had to be picked from a menu each time it was used) and the primitives provided for the maze demo rather limiting (the only conditional was testing one of the neighboring cells for having a wall).
Blockly may be a nice demo of what can be done in the browser these days, but it is way short of Scratch in terms of fun, education, or usefulness. If it is ever going to go anywhere, it needs to be an order of magnitude better.