OLPC and Firefox OS are not examples of projects that pushed the idea of an OS and application stack that could be understood by a single person. To get a better idea of what Alan Kay has been working towards I'd recommend checking out the STEPS project.
The software for both OLPC and Firefox OS were both based on Linux. Is there anything that made them more approachable on the low level than any other Linux distro?
I say that they were the closest, not that they were complete implementations of the vision.
Firefox OS had a particularly hackable UI layer. You could install webpages as if they were apps (all assets stored locally), bypassing the need to get your app into a curated store. Writing new drivers in Javascript could have come later.
