Solve Me Mobiles - Solve ready-made mobiles or create your own
Game About Squares - Figure it out by playing the game
ReFRACTIONS - Very interesting; can get challenging if you stick with it.
Drop 10 - Not hard, but fun; switch between timed mode and infinite mode.
Pearls - This is really a version of the classic game NIM.
Jelly - Can you get past Level 3?
Crossed Lines - I suggest you start with "Child's Play".
Mathematics is the Study of Patterns - Match patterns; build patterns.
The Game of Set - Originally a card game, now available digitally - cards are still the most fun.
Set Tutorial - how to play Set
Set Online - a new puzzle every day
2048 - I love this game. I've scored 4096!
Logo - learn computer programming
Ray-Ray - this one is cute
Minesweeper - recommended by students at Keewaydin