FPSPOT

FPSPOT is a free browser-based calculator site. Age and date tools include chronological age, age difference, age on a specific date, pet age and a printable 2027 calendar. Numbers and money tools cover percentages, percentage increase and decrease, percentage off, percentage difference, rounding and CPM, plus NPV (which also covers gross rental yield) and IRR.

Gaming tools include eDPI, cm/360, mouse sensitivity, DPI, FOV, and converters for Valorant, CS2 and Rainbow Six Siege. The site says there is no sign-up, inputs are processed in your browser, and nothing is uploaded.