Logic Masters Deutschland e.V.

Route 66, by James Sinclair

Normal sudoku rules apply, and all clues are standard.
Negative constraint: digits in orthogonally adjacent cells cannot have a 1:2 ratio.
Renban lines: purple lines contain a non-repeating set of consecutive digits in any order.
Quadruple circles: a digit inside a white circle appears in one of the four cells surrounding that circle.

SudokuPad

Since I haven't linked to it here before, I wanted to mention the Artisanal Sudoku book, which will be published March 17 and is available for pre-order now. The book features 150 variant sudokus, including 75 new puzzles and 75 favorites from the first four years of my newsletter. I put a lot of work into it, and I'm really excited for it to finally be out there :)