• Kahoot - a 'game show' style website where you can create quizzes for students to check their understanding and/or practice essential skills.
• Purple Math - free resources on a variety of concepts; geared toward high school teaching
• Math-Aids - free worksheets organized by topic, ranging in skill level
• Math is Fun - resources on a variety of concepts; organized by topic; ranging in skill level; written in accessible language
• Desmos - graphing and scientific calculator; allows students to analyze multiple equations on the same grid; ready to use activities for the class; geared toward high school teaching.  This is also an app!
• IXL Math - practice questions for all grade levels in a variety of concepts.  Cost to use all the functions of the website.
• Kuta Software - Cost to obtain the customizing software.  Free, ready-made worksheets available online; organized by topic
• Photomath - Solves math typed or written, with full solutions.  Free to use on typed math, cost to use on written math.
• The Thinking Classroom - Learn more about the benefit of vertical, non-permanent surfaces & find loads of rich problems for students to work on.
• EstiMysteries - working to develop students' estimation skills