Calcucil is a free Android game developed by Rubén Pérez that challenges your mental math skills. The game consists of true or false operations that you must solve as quickly as possible. The more correct answers you get, the harder the next ones will be.

The game includes addition, subtraction, multiplication, and division operations, and each one has a different time bonus or penalty. For example, if you answer a multiplication correctly, you'll earn 3 seconds, but if you answer it incorrectly, you'll lose 2 seconds. The game keeps track of your time, and you can accumulate time with each correct answer to achieve the highest score possible.

Calcucil is a fun and engaging way to test your math skills and challenge yourself to get better. If you're looking for a fast-paced math trivia game, then Calcucil is definitely worth a try.