Logic Masters Deutschland e.V.

Normal X-Sudoku rules for an 8x8 grid apply (put the digits 1-8 without repeats in every row, column, box, and both major diagonals).

The lines denoting the "X" also function as region sum lines (segments of a line divided by box boundaries must sum to the same value).

The circles joined by lines function as both double arrows (the sum of the digits on a pair of circles must be the same as the sum of the digits along the line connecting them) and between lines (the values of the digits along the lines must be between the values of the digits in the circles at the ends).

In addition, all of the cells covered by a double arrow/between line form a single extra region, in which repeated digits are not allowed.

That number 6 outside the grid is both an x-sum (the first x digits, where x is the first digit in that row, sum to 6) and a sandwich sum (the digits between the 1 and the 8, not including those digits, in that row sum to 6).

SudokuPad link here