My understanding is that they are non-existent, and people are still arguing over the design and implementation details. But if you've got the skills, you can

My understanding is that they are non-existent, and people are still arguing over the design and implementation details. But if you've got the skills, you can help. You know what it's supposed to do. Chances are, whoever stops bickering and builds one first wins. I'm going to see if I can get my local hackerspace to help me experiment and build at least some sort of prototype.