3.  Khan Academy is the granddaddy of limitless learning. The offerings on this website have expanded exponentially due to Gates’ funding, and now include Common Core State Standards.  Now teachers have the ability to set up classes to not only coach students, but to use videos in the classroom for direct instruction.  If a teacher or parent sets up a class, like Learn Zillion, now they have an opportunity for follow up formative assessment and guided practice.  Most importantly, while Sokikom addresses K-6 math, and Learn Zillion K-12 math and language arts, Khanacademy provides instruction in a wide variety of topics, from chemistry, finance, biology, math, etc. 

See short video about khan Academy: