Scratch

This is a really cool level creator.

It's
~snap-to-grid
~colors gray-green-red-blue-purple
~design of blocks looks pretty cool.

Unfortunately, you can't test out your level, but the good things about that are:
-you can have the colors represent whatever you want
-you can use whatever scripts you want for the main sprite

For the levels, just take a screenshot and upload the picture to your project.

Here it is:
http://scratch.mit.edu/projects/Luxturna/2325304

Scratch on!