In an introductory statistics course, it is better for students to spend time understanding the concepts and interpreting the results rather than wading through lengthy calculations.
To this end, I have developed an Excel workbook, Stats Companion, that can perform many of the calculations required in an introductory statistics course - summary statistics, boxplots, frequency distributions, histograms, confidence intervals, correlation and regression, scatter plots, normal probabilities.
Though certainly not as powerful as Minitab, it is free. The only requirement is that the user be familiar with Excel - mainly to copy data from another Excel file to Stats Companion.
The Stats Companion website contains information about downloading the workbook and getting it to run properly. Since it contains macros, users have to understand how to enable macros. They also have to be able to add Add-Ins to Excel. Details on these topics and other installation recommendations are on the web site.