Small calculators that answer one question properly and then get out of the way. No signup, no adverts, nothing to install.
More are coming, roughly one every few weeks. What gets built next is decided by the vote at the bottom of each tool, so it is worth using.
One person building a free tool every few weeks. The next one goes to this list first.
Being straight with you: these are experiments. Some will be abandoned and the bigger thing behind them may never get built. One email a fortnight at most, unsubscribe in a click, no selling. You will get a confirmation email first — your address is not added until you click the link in it.
Because I am finding out which of them people actually want. Each one is a real tool that has to be useful on its own, and each is also a question: does anyone need this? Some will be kept and improved. Some will be dropped. The longer version is here, including what happens to the ones that get dropped.