These tools are for readers in the United States. Four of them are about money in retirement: the RMD calculator for required minimum distributions and inherited IRAs, the IRMAA calculator for Medicare surcharges, the Social Security calculator for how much of your benefit is taxable, and the backdoor Roth calculator for the pro-rata rule on Form 8606. The overtime calculator turns hours into pay and estimates the federal qualified overtime deduction, and the military time converter handles the 24-hour clock, shift hours and US time zones.
Each page names its sources and the date they were checked, and says plainly what it does not cover. They give estimates from published rules, not tax advice. Everything runs in your browser: nothing you type is uploaded, and there is nothing to sign up for.