This one started with LinkedIn. They have a daily logic puzzle called Queens and it is genuinely good fun. One a day, however, is not quite enough for a certain type of person, and the leaderboard had developed a noticeable population of individuals claiming to solve nine by nine boards in four seconds. Whether that is humanly possible is left as an exercise for the reader.
So I built my own version. Queens With Friends is an open-source logic puzzle engine based on the same core concept: place one queen in every row, column, and colour region, with no two queens touching, including diagonally. The interesting part is what sits around that core. You can build your own boards, generate random ones at various difficulty levels, and share them directly with friends via a link that contains the entire board state. No server required.
There is also a Solve tab which steps through the solution one move at a time and explains the reasoning behind each one. If you want to understand the logic rather than just guess your way through it, that is where to start. It uses a heuristic deduction engine that works through puzzles the way a human would, which makes the explanations actually useful rather than just a list of coordinates.
It is an early release and there are likely a few rough edges still to find. But it is playable, shareable, and considerably more satisfying than wondering how someone finished a nine by nine in four seconds.