Ed Brandao

Math is real:

Why word-problems are not the solution to math real-world math education:

https://mathwithbaddrawings.com/2015/01/28/the-word-problem-problem/

Math visualizations:

http://metrocosm.com/about/

Teach Now related:

Differentiated, adaptive Common Core-aligned problems (I only did explore math problems):

http://www.ck12.org/assessment/ui/browse/index.html

More adaptive learning by US Team Math Olympiads coach Po-Shen Loh:

https://www.expii.com/about/mission

Curated problem sets, organized by theme and grade:

http://www.aplusclick.com/

I get interesting insightful problems from the Eton College entrance examinations:

http://www.etoncollege.com/KSpapers.aspx

PLN:

All fora in the Art of Problem Solving. The books are great for differentiated instruction and to get new ideas.The community is really helpful. There's a wealth of resources in there, too long to list. Great for all math instructors.

http://artofproblemsolving.com/

Terry Tao's blog is an amazing resource. He is the foremost mathematician of our time and often shares his thoughts on math education and research. As a teacher, I think I should at least have an idea of what the current mathematical frontier is. Comments to individual posts are sometimes as good as the post itself.

https://terrytao.wordpress.com/2010/10/21/245a-problem-solving-strategies/

Problem driven instruction:

Project Euler has been around for a while. It posts easy to understand problems (number theory mostly), which can initially be solved by hand and later using a programming language of choice. A good introduction to computer science and number theory, and something I would like to adapt to high school math one day. Maybe calculators could be replaced with computers + basic coding skills?

https://projecteuler.net/archives

Desmos is a step in that direction,

https://www.desmos.com/about

as is

https://www.geogebra.org/about,

but not quite there yet.

I also like MIT's http://mathlets.org/

And also interactive math:

http://www.intmath.com/

Becoming a headteacher by leading a challenging school:

http://www.future-leaders.org.uk/programmes/future-leaders/

In case I missed anything, a list of curated resources (like r/random but occasionally useful), because it's refreshing to look at something other than math!

http://www.randomusefulwebsites.com/