Teachthought describes this as "While the site is simple a crudely interactive graphic with links to videos, it has, in one fell swoop, creatively curated some of the most compelling and engaging "problems" in mathematics. From Benford's Law to French Numbers, to whether or not zero is an even number, it frames the content area of math-which is often riddled with rote practice of very traditional arithmetic and formulas-in a problem-based learning kind of approach.
Fantastic resource for bell ringers, test questions, math project-based learning ideas, or as a model for students to curate their own curiosities about the incredible-and poorly marketed-world of mathematics."
This is a fabulous resource with practical lesson plans, valuable resources, and more. I've used several of their lessons. There's an interesting story behind how they "earned" the money to remain free.
Calculation Nation® uses the power of the Web to let students challenge opponents from anywhere in the world. At the same time, students are able to challenge themselves by investigating significant mathematical content and practicing fundamental skills. The element of competition adds an extra layer of excitement
Vicki Davis' YouTube channel. She is a technology teacher in Georgia, and has many practical, useful tips, including for blogging, evernote , diigo, YouTube, and other tools.