With over a million high quality educational videos, games, assessments and courses, OpenEd (http://opened.io) recommends resources for any given topic that a K-12 teacher is covering, especially when teaching to the Common Core State Standards. Originally intended to be the largest educational resource catalog for the Common Core, it has since become the largest K-12 educational resource catalog of any kind.
OpenEd is available with both an open API for searching OpenEd's resources and for contributing to it. Many other K-12 edtech companies are using OpenEd's APIs for both purposes.
OpenEd's revenue model will be centered on teacher paid subscriptions, which are requirement assessments and analytics of student performance combined with resource use. It also includes percentage of paid content revenue for content publishers with paid content.