Actually, if niche/small-volume makers are allowed in the discussion, there’s this:
Released January 2009, if I’m not mistaken, about six months before the ASUS. It’s an implementation of the Intel “Classmate 2” platform, which is more or less a netbook.
And about the Apple-based netbook platform… I think you might be waiting a mighty long time to see anything along those lines emerge. (Of course, if it’s cheap, I wouldn’t mind being proven wrong!)