There have been several in development over the past several years (probably since late 08)
The closest to being near production I think is Mirasol, and for a while now Amazon has been rumored to be using it on the next Kindle, so has B/N though...
I also know of a couple alternatives to Mirasol that are in development now, but I'll let some of the smarter members chime in on them
*poke poke*