This site has two Sudokus, one or two Killer Sudokus, and many Calcudoku puzzles every day.

On Calcudoku

Early 2009, I read about KenKen (also known as Calcudoku) in the
New York Times, and decided to write a program that creates similar puzzles, and put them online.
Calcudoku puzzles are similar to Sudoku, but also require some basic math skills to solve.

The rules are:

the 4×4 puzzle uses the numbers 1-4, the 6×6
the numbers 1-6, and so on

in each row and in each column each digit can
appear only once (just like in Sudoku)

each "cage" (the blocks with the
thick border) shows a result and an operation (addition: +, subtraction: -, multiplication: ×,
or division: :). The operation applied to the numbers in the cage should
produce the result shown. Note that for subtraction and division the order is not fixed (!)

Look at the solutions of earlier days to make things clearer.

Brief explanations of the special operators (e.g. ^ for exponentiation) is given
below the puzzles with these operators.

You can solve the puzzle on the page using the arrow and number keys, or using the mouse.
Use the spacebar to clear a cell.
Use backspace to undo a move. Press '=' to highlight the number in a cell.
In the largest puzzles (10x10 Calcudoku puzzle (every Tuesday and Friday) and 12x12 (every Sunday and Thursday)), simply
press 1 then 0, or 1 then 1, or 1 then 2 to enter 10, or 11, or 12. You can also use the a, b, and c keys to enter 10, 11, or 12.
Press the Shift key and a number to store it as a guess.

You can now do the puzzles on Facebook
(you can combine your facebook account with this one, and keep using both).

You can also solve the puzzles on the iPhone/iPod Touch/iPad and the Kindle 3.

Every puzzle has a single solution.

This type of puzzle is known as Calcudoku, Newdoku, Rekendoku, MathDoku, Kashikoku-Naru, KenKen, Kendoku, Sumdoku, Calkuro, K-Doku, Keen, NekNek, CanCan, Square Wisdom, Emono,
Minuplu, LatinCalc, Yukendo, ArithmeGrid, Hitoshii, Inky, SquareLogic, TomTom, and if you know of any other names, let me know :-).
The "no-op" puzzles are sometimes called "Mystery Calcudoku".
Of these names, "KenKen" and "KenDoku" are trademarks of Nextoy LLC. Note
that this is a hobby site, and is not affiliated with Nextoy nor their brands.