Desmos
Interactive graphing calculator and activity builder for exploring algebra, geometry, and more.
https://www.desmos.com

Khan Academy
Video tutorials and interactive practice from early math through calculus.
https://www.khanacademy.org

GeoGebra
Dynamic geometry, algebra, statistics, and calculus tools.
https://www.geogebra.org

Mathigon
A visual and interactive math textbook that makes learning math engaging.
https://mathigon.org

IXL Math
Standards-aligned personalized math practice.
https://www.ixl.com/math

Flocabulary (Math section)
Educational hip-hop videos that teach math concepts in a fun and rhythmic way.
https://www.flocabulary.com

Boddle Learning
Math practice through an engaging video-game style platform (great for elementary & middle school).
https://www.boddlelearning.com

Nearpod (Math lessons)
Interactive math lessons with polls, quizzes, videos, and VR.
https://www.nearpod.com

Illuminations (by NCTM)
Provides lesson plans, activities, and interactive math tools.
https://illuminations.nctm.org

Zearn
Comprehensive math curriculum with built-in digital lessons and practice.
https://www.zearn.org