cZeus Puzzles (cZeusPuzzles.com) are clever mixes of Sudoku style logic, attention and memory, plus maths skills added.
The Baixaki site from Brazil calls it "Sudoku with maths" - http://goo.gl/EAArWz
There are currently 5 classes of puzzles (from easy Mortal to very hard Titan puzzles). All the tiles on the board are numbers from 1 to 9, clues are given in the form of addition or multiplication of adjacent tiles. Few simple rules ensure that there is a unique solution to each puzzle.
Would be keen to see what you think of cZeus puzzles.
drmaths