MinuPlu
MinuPlu was invented 2004 by the Japanese math teacher Tetsuya Miyamoto under the name 賢くなるパズル (Kashikoku Naru Puzzle, "Puzzle that makes you clever"). While it is similar to Sudoku, it is still a completely different puzzling experience. Other names for this type of puzzle are Ken Ken, KenDoku, MathDoku, or CalcuDoku.
Rules
 All cells of a MinuPlu have to be filled in with numbers. The possible numbers range from 1 to the size of the MinuPlu. For example, in a 4×4 MinuPlu there are the numbers 1, 2, 3 and 4.
 Each number must appear exactly once in each row and each column. (However, in contrast to Sudoku, there are no blocks where this must be fulfilled as well.)
 Each region surrounded by a thick line contains an arithmetic operation (addition, subtraction, multiplication or division) and a result. The numbers in each such region must yield the indicated result when combined by the corresponding operation.
Note:
 Regions may contain numbers more than once as long as rule 2 is not broken, see region [36 ×] in the above example.
 Regions with subtraction (−) or division (÷) consist of exactly two cells. There are no special rules determining the order of the numbers therein, see region [2 ÷] or [1 −] for example.
Solution techniques and tips

For each region: Think about what possibilities exist and write these possibilities down, e.g. 1 = 4 − 3 = 3 − 2 = 2 − 1.
By the way: You can make annotations even in the online game! (Click on the white area outside the puzzle, enter an annotation and move it to the desired place.)  If the regions are larger than two cells: Do all your considerations on a systematic basis to be sure to find all possibilties for the region.
 Make small annotations inside regions whenever you know which numbers there must be but don't know the exact order. This can help you to solve other cells outside that region. In the example, you see a part of a 4×4 MinuPlu. The numbers 2 and 3 are certainly in the bordered region. While we do not know the exact order, we make an annotation inside the region. This annotation helps us to see that the cell with the blue circle must be a 4.
Tips for Playing MinuPlu online
Arrows up and down: Go to previous or following days with other puzzles.
Arrows left and right: Switch between the MinuPlus of one day.
The bullets show you the level of difficulty (easy, medium, difficult).
By clicking in a cell, you can select the desired number. Choose 0 to erase a previously entered number.
By clicking on the white area outside the MinuPlu, you can enter annotations. This is very useful for large MinuPlus. Pressing Enter adds a new line. Pressing Escape (top left on the keyboard) quits the input mode.
You can move your annotations (even into the MinuPlu) by dragging it to the desired position with your mouse.
In addition, you can view the solution and decide whether wrong numbers should be shown in red.
If you want to play against time, use the stopwatch.