I am tackling a related challenge with Digraph, an app I'm working on [0]. My project is focused less on providing an infrastructure for learning and retention, and more on simply organizing the vast amount of information that each of us reads every day, month and year into a collection that is coherent and growing and that builds upon itself.
The long-term vision is a crowd-sourced alternative to search engines like Google and Bing. But the short-term focus is on something targeted and immediately useful.
> If the company that runs your PKR goes out of business you’re entire education might be in jeopardy.
I'm dealing with this problem in part by making the Digraph source available under the MIT license.