Least Givens Sudoku
This version of sudoku has much fewer givens than ordinary sudoku due to the added constraint that cells that touch horizontally or vertically cannot contain the same value as each other, or one more or one less than neighbouring cells. So if a particular cell contains 4, then cells touching it cannot contain 3,4,5.
In addition, these constraints wrap around the edge of the puzzle, so from the top right cell for instance the top left cell is constrained, and the bottom right cell, in addition to its immediate neighbours on the grid.
Here is a link to the start position of the puzzle in PDF. This one is a 12 givens sudoku, though this variant can be made with fewer given cells, down to eight.