Unfortunately, I'm not aware of any. Would be quite interested as well. If I find some time,I might actually take this opportunity to try and learn doing something like this myself. Unfortunately, I don't know when i might have that time, definitely not before autumn... :/
Onyx do have an sdk somewhere online which had some sources. I guess the kernel would need to be open source as well due to the gpl. I don't know how much else of the system could be open source, you'd probably have to ask them.
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