chessGMIn Rush Battle you and other players get the same chess puzzles for 3 minutes and see each other's scores live. The highest score when the clock stops wins.
You can also challenge friends in a room, for up to four players. If you would rather practise alone first, Puzzle Rush uses the same kind of puzzles against the clock.
Rush Battle is a good way to train speed and pattern recognition under a little pressure: the puzzles are rated, so they match how well you usually do, and the live scoreboard shows at once how you compare with the others in the room.