The CK-12 Foundation is a California-based non-profit organization which aims to increase access to low-cost K-12 education in the United States and abroad. CK-12 provides free and customizable K-12 open educational resources aligned to state curriculum standards. As of 2022, the foundation's tools were used by over 200,000,000 students worldwide. CK-12 was set up to support K-12 Science, Technology, Engineering, and Math (STEM) education. It first produced content via a web-based platform called "FlexBook."