You won’t believe it—somebody actually created a game whereby all grammar sticklers out there can put their knowledge of and speed with grammar rules to the practice!
The way the game works is that you’re presented with “poorly written student papers” taken straight from Wikipedia and you have to find the errors that have been inserted, all on a timed counter. Then you’re given a score based on how many errors according to standard rules of grammar you managed to spot and the amount of time it took you to do it.
For more details and to download, check out this full review.