I've been working on a newish variant of Sudoku called Binku. It combines the traditional Sudoku rules and adds the rules from a game called Binario/Takuzu (with 1-4 as one color and 5-8 as the other color).

A sample puzzle can be found here: https://sudokupad.app/23x300ggzn

It's been well received by the (very kind!) Sudoku/puzzle communities, so I'm working on throwing a nice interface on it that fits the rules a bit better. I've found about five other examples of others doing a variation of this ruleset before in one way or another, and it's been fun trying to see how hard/deep I can get this puzzle to go.