An offline version of Khan Academy.
A free lightweight solution providing high-quality education where you need it most.
Though this software is unofficial, it is known of and approved by the official website.
disliked - because it has no concept of building a larger topic of things to work on, and showing an easy path to progress through them. Needing to pick through a large number of topics, sub-topics and quizzes and then manually and repeatedly going back into that list is inexcusably frustrating.
Once installed it's seen at http://127.0.0.1:8008/