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Standard deviation, z-scores, confidence intervals, dice odds — this is the number-crunching shelf. Paste in a data set and the mean, median and mode tools describe it, the standard deviation and variance calculators measure its spread, and z-score and percentile tools place a single value inside a distribution. On the probability side there are calculators for coin flips and dice rolls, binomial and normal distributions, permutations and combinations, and a p-value checker for hypothesis tests. Every result comes with the intermediate steps, because in statistics and probability the method usually earns more marks than the answer.
Most visitors are students working through an intro stats course the night before a problem set is due — joined by researchers verifying a margin of error, board-game and poker players pricing an outcome, and analysts double-checking a spreadsheet formula.
The classic mistake to avoid: sample and population standard deviation are different formulas. Dividing by n − 1 instead of n corrects the bias of small samples, and it is what most coursework expects. If your answer is close but wrong, check this first.