It hasn't been released yet (still in development), but that is exactly what my employer (Knewton) is working on. It is still mostly under-wraps, but you can sign up to stay informed here:
Don't hold me to this (I'm on a different team), but I think the goal is a closed beta by the end of this year, primarily for the content creators. This is to seed the platform with lots of content so it isn't empty when it launches.
Early next year the platform will begin to open up to the general public.
http://learn.knewton.com/join