AAA Math: http://aaamath.com/
Calculator Soup Online Calculators: https://www.calculatorsoup.com/
Desmos Graphing Calculator: https://www.desmos.com/calculator
Math History: https://mathshistory.st-andrews.ac.uk/HistTopics/
Math Page: https://themathpage.com/Arith/arithmetic.htm
Math Portal: https://www.mathportal.org/index.php
Mathway Algebra: https://www.mathway.com/Algebra
Metric Conversions: https://www.metric-conversions.org/
Wolfram Mathworld: https://mathworld.wolfram.com/