Statistics apps 

Generate data and see how it looks on a  normal QQ plot.  Adjust skewedness and tail length to see how non-normal data appear.

Violate normality and/or equal variance assumptions; see what happens to sampling distribution of t-stat and Type I error rate.  Switch between two- and one- sided tests.  Compare Student's and Welch's tests.

Set effect size and sample size for a two sample t-test; see what happens to sampling distributions of the test statistic and p-value

Simulate bivariate data and manipuate correlation.  See how slope for simple regression depends on correlation and the standard deviations of x and y.

See the effect of "optional stopping" (checking the p-value as data are collected; stopping if p <0.05) on the sampling distribution of the t-test statistic

Plot and calculate probabilites from the t-distribution by supplying an estimate, standard error, and hypothesized value.

Plot and calcuate probabilities from the normal distribution; compare x and z axes; find z given probability.