Piksi GPS (http://www.swiftnav.com/piksi.html) and the more recently Reach GPS (https://www.indiegogo.com/projects/reach-first-affordable-rt...) do offer this kind of functionality, but it is still tough to do, so props to the Texas team for democratizing $10,000 technology.

However, I wish some of these guys would show us the initialization procedures. In my experience trying to get an RTK level solution with an L1 only GPS receiver (read: cheap) is impractically hard. Then once you have it, you can lose it with the slightest change in the number of satellites available (i.e. if you go under a tree or next to a building). However, my experience is now over 3-4 years old, maybe we've come a long way.