Yajilin

[from Nikoli website]

Draw a single line with a loop following the next rules:

1. Lines must pass through the centers of cells horizontally or vertically and never cross, branch off, or go through the same cells twice.
2. Cells where the line is drawn must not be black.
   
3. Black cells must not touch each other horizontally or vertically.
   
4. Lines don't go through numbered cells. Numbered cells cannot be black cells.
5. Numbers represent how many black cells are at the direction of the arrow.

Solution:

ALTERNATING WEAPON CHESS

No-capture chess plus:

First player makes one move, then players make series of two moves until
captures are made, whereupon the series become of length three, etc.

Captures may be made as a series of one move only. The first capture
may be of either type, hand-grenade(*) or machine-gun(:), (which must
make the maximum number of takes available for that particular move);
and after that each player's capture types must alternate.

During a series of non-captures it is permissible to play a piece into
a position where it could make either sort of capture but does not do so,
at the mover's choice. Declaration of ambiguous capture type is unnecessary.

r . . . . Q . .     |  1. e4               11. Ng5::
. p k r . . b .     |  2. e5 Nc6           12. Bf6:
p . p . . R . .     |  3. Nf3 c3           13. f4* +
. . N p . . . .     |  4. d5*              14. Kf7e7d7c7
O . . O . . . .     |  5. Bb5: +           15. Nd2b3c5 Qg4
. . O . . . . .     |  6. c6:              16. Be6 Rf7d7 h6
. O . . . . O O     |  7. 0-0 d4 a4        17. Qg8::
R . . . . . K .     |  8. Be7 Nf6 O-O      18. Bg7*
____________________'  9. Bh6**            19. f5f6f7f8Q Rf6
                      10. Nh7*             20. resign

LOVE-Y

LOVE-L modifier:
Along with one's own stone one must play an opponent
stone as (Euclidean) close as possible to one's own.

          .            1.   n6  o5    m5 n4
         . .           2.   g7  f6    h6 g5
        . . .          3.   f8  e7    k7 m7
       . . . x         4.   l10 m11   j10 k11
      x . . o o        5.   j8  i9    i7 j6 !
     o o x . x .       6.   h8  g9    l8 n8
    o x o o x . .      7.   resign
   . x x x O X . .     8.  
  . . o o . . . . .    9.  
 . . . . o x . . . .  10.
. . . . . x o . . . . 11.  
abcdefghijklmnopqrstu

The 5th move for the second player finishes the game abruptly (a kind of mate in 6).

Ripple Effect

[from Nikoli website]

The areas, divided by bold lines, are called "Rooms". Fill in all empty cells with numbers under following rules:

1. Each Room contains consecutive numbers starting from 1.
2. If a number is duplicated in a row or a column, the space between the duplicated numbers must be equal or larger than the value of the number.

Solution:

Nonogram (aka Paint By Numbers)

[from havards website]

1. Paint some black cells such that they obey all numbers:
   
2. Each number determines a number of consecutively filled squares (called a cluster).
3. Each number sequence (row or column) shows how many clusters are there and the cluster sequence (naturally, each cluster is separated by, at least, one empty cell).
   

Solution:

To read more, go to the Wikipedia entry. Also check a similar puzzle, Solitaire Battleship.

Black Cells

[from Nikoli website]

1. Place black cells according to the next rules:
2. Each number on the board represents the sum of white cells from that number to black cells or outer frame, horizontally and vertically.
3. The cells which include numbers are always white.
4. Black cells must not touch each other horizontally or vertically.
   
5. All white cells must be orthogonally connected.

Solution:

Tentai Show

[from Nikoli website]

1. Draw a bold line over the dotted line and divide the board into blocks.
2. Every block must have horizontal and vertical symmetries with a star at its center.

Solution:

Number Link

[from Nikoli website]

1. Connect same numbers with continuous line.
2. Lines must go through the center of a cell horizontally or vertically and never go through twice the same cell.
3. Lines cannot be crossed, branch off or go through number's cells.

Solution:

Divide by Box

[from Nikoli website]

1. Divide the grid into rectangles.
2. Each rectangle contains only one number.
3. The number indicates how many cells are contained in the rectangle.

Solution:

Heyawake

[from Nikoli website]

The rectangle, divided by bold lines, is called "Room". Each number indicates how many painted cells exist in its room, while no number rooms may have any number of painted cells. Paint cells under following rules:

1. White cells must not exceed two rooms in a straight line.
2. The painted cells must not be orthogonally connected.
   
3. White cells must not be (orthogonally) separated by painted cells.

Solution: