PhET provides free interactive math and science simulations that engage students through an intuitive, game-like environment where students learn through exploration and discovery.
Founded in 2011 at the University of Arizona, Illustrative Mathematics provides instructional and assessment tasks, lesson plans, and other resources for teachers.
OpenCurriculum curates and organizes material from sites such as teacher blogs and lesson material publishers. Math teachers can create lesson plans and explore the 5,000-document library to use as lesson materials.
Blossoms provides video lessons for high school math and science. Every lesson includes video segments, a teacher’s guide, downloadable hand-outs and a list of additional online resources relevant to the topic.
CK-12's FlexMath provides a student-centered approach to Algebra proficiency. It provides lessons, interactive practice, adaptive assessment, and scaffolding for struggling learners.
Algebra2go is a free unrestricted collection of pre-algebra and algebra related study materials designed to address the various dimensions of student learning.