Some Useful Web Based Tools for Math for Elementary Education

Conceptua math: fraction tools
https://teach.conceptuamath.com/app/tool-library

Thinking blocks: Modeling word problems and operations with fractions, ratios, and whole numbers
http://www.mathplayground.com/thinkingblocks.html

Math Playground tools including Cuisenaire rods,  pattern blocks, geoboard, a function machine, transformations, a pretty good spinner, fraction-decimal-percent scales, an algebra balance scale, transformation tool, long division... rather a lot of useful stuff!
http://www.mathplayground.com/math_manipulatives.html

In particular, I've decided I rather like professor x and the factorbots (though I don't know how to make it into a good lesson)
http://www.mathplayground.com/professor_x_and_the_factorbots/index.html

Multiplication blocks is great for factoring
http://www.mathplayground.com/multiplication_blocks.html

Shodor interactive
http://www.shodor.org/interactivate/activities/

Animal Rescue is pretty good for negative number visualization:
http://www.crickweb.co.uk/ks2numeracy.html

The Math Cats tessellation pictures are kind of fun
http://www.mathcats.com/explore.html
This looks like a useful list too:
http://mathcats.com/mathexplorations/

I also like the games at Manga High:  https://app.mangahigh.com/home/games

and Lure of the Labyrinth: https://labyrinth.thinkport.org/www/ I've decided the first set of puzzles (the cafeteria puzzles) would be good when working with ratios. (maybe)

Glencoe has some pretty good virtual manipulatives:
http://www.glencoe.com/sites/common_assets/mathematics/ebook_assets/vmf/VMF-Interface.html

These are good virtual base 10 blocks
https://www.coolmath4kids.com/manipulatives/base-ten-blocks
the other virtual manipulatives look promising too:
https://www.coolmath4kids.com/manipulatives/base-ten-blocks

good number line and a good base 10 blocks app
https://www.mathlearningcenter.org/resources/apps

More virtual manipulatives
https://www.symbaloo.com/mix/onlinemathmanipulatives

Pretty good base blocks activities
https://www-k6.thinkcentral.com/content/hsp/math/hspmath/na/commol
n/itools_int_9780547584997_/basetenblocks.htm


Shape sorter for geometry properties
http://illuminations.nctm.org/Activity.aspx?id=3581

Dreambox. I like the third grade number line tools (though they need a little instruction)
http://www.dreambox.com/teachertools

 I like this decimal and fraction sum estimator
https://teacher.desmos.com/activitybuilder/custom/57d85047b9d7e48a07626b70