I have developed two programs for my own use, but they are being used by other people.
Manyex is a program to prepare exams and quizzes using the Tex/LaTex system. From a base of possible questions, and a configuration file that tells the system what type of exams you want to set, you can create different permutations with different questions and the questions permuted within the exams.
It is written in C.
More information about manyex - Download manyex
ODStatistics is a set of OpenOffice.org Calc spreadsheets with different statistical tools. So far it includes only descriptive analysis. I wrote this package for my course in Data Analysis at Universitat Pompeu Fabra, and it is inspired in XLStatistics, a set of Excel macros with a much more complete list of statistical tools written by Rodney Carr.
More information about ODStatistics - Download ODStatistics