I am a late arrival to discovering this game. I was looking for alternatives to PowderToy but despite the differences between the two in terms of genre I get the same appeal behind Cresent Loom like I do PowderToy. It's a biology sandbox in this case.  

You can create your own underwater beasties out of muscle, bone, fins, jaws, eyes and neurons like a mad scientist but I get the idea behind the sandbox. It teaches me how I am able to walk, form sentences to type out and how my reflex action works without me having to plan the many motor control mechanics behind it. I just will it to happen and neurochemistry does the rest behind the scenes. 

There's different ways to play the sandbox. There's a tutorial that's short but sweet, a testing area to experiment without any hassles from other beasties, a racetrack of sorts and more. The developer Olive says this version is still being used in many classrooms as student assignments, and there may be a 2.0 down the road.