StarLogo Nova is another MIT project. It's block based like scratch, but I personally find it much nicer to use, and it allows (I think) for more complex programs. It is more simulation oriented than scratch, but you can still make just about anything with it. Also, it has a flying turtle for a logo:
It's got a nice setup for classes - each user has a profile with a public and a private gallery. You can add collaborators to projects, set up some form of "class" on the system, though I don't know quite what that entails, etc.
Here's a screenshot of the coding environment with some code for a project I did in it:
On the left, you have a menu with the different coding blocks, the drop down has categories very similar to those in scratch. The tabs on top of the coding section are basically for the different "agents" and for the "world". This program, if you're wondering why there's a "Killers" tab, is to simulate an epidemic. There's support for all sorts of things - procedures that return values, movement of "turtles" which are basically robots on the screen, etc.
Here's a screenshot of the section of the screen that shows the result of your program:
This shows the level of complexity you can get too - you can have output graphs and number boxes, input sliders, etc. You can also keep it very simple - the two things that are pretty much always there are the "setup" and "forever" buttons. This screenshot was taken right after "setup" was pressed - it initialized the turtles, widgets, breeds in the right proportions, etc.
I'd definitely recommend this language.