SimSam is a program to simulate a survey. If you carry out a survey, you select a sample from a population. Then you use the sample data to estimate charactersitics of the population.
SimSam simulates samples from a populations. By repeating the selection of the sample a large number of times, and computing an estimate for the population mean for each sample, the distribution of the estimate can be portrayed on the screen. By taking a look at this distribution, it becomes clear how well an estimation procedure is able to estimate the population mean.