You've been looking for something similar, discovered that this "something similar" exists, yet the Apple logo puts you off? A used iPad that can run this is probably a couple hundred dollars.

Now, perhaps I've misinterpreted your question, and you'd just like a list of alternatives to keep your options open. I've not looked really hard, not having any kids and all, but there seems to be a dearth of options that meet the (IMO) high bar Playgrounds has set. Me, I wonder if the 2nd-best alternative isn't an old machine with QBasic on it. I just don't see anything else out there that doesn't start with "Step 1: Let's learn about dependency trees!"