I've written one which is still under development. It currently works on x86 and ARM

Getting over the first part is the hardest. You just have to try a lot and read alot. If there's anything specific just send me a PM or contact me on jeppesoftware@hotmail.com

There's a bit about it here, though no source yet. I'm still looking for a way to get a source control repository http://j-software.dk/