Calculator X started as a keyboard-friendly arithmetic calculator. It has grown into 17 small tools for the questions that come up during a normal week: whether to pay someone to do a task, what a subscription really costs over time, how to split a dinner bill, or whether a piece of furniture will make it around a corner.
Each calculator has its own page and explains the assumptions behind its result. The original arithmetic calculator is still there too. Try one and tell me which question I should turn into a calculator next.