QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.

FroZenLight interrelates line arts, mathematics, and cryptography. Circular shaped mirrors which are arranged in a grid-like manner reflect a light ray according to the reflection law of geometric optics. While random positions of the light source produce chaotic reflection patterns, it is possible to position the light source so that beautiful symmetric reflection patterns are created.

MonoDecrypt uses pattern matching and its knowledge about character frequencies in order to decrypt messages encoded with a monoalphabetic substitution cipher. MonoDecrypt can decrypt texts of any language, as long as it has sufficient information about the language. Depending on the information you give it, the tool decrypts about 50%-100% on its own. Then you can decrypt the remaining data by filling the gaps or correcting bad guesses. MonoDecrypt can also encrypt texts using monoalphabetic substitution.

The Item Response Theory (IRT) library is a set of functions to estimate the items and abilities from the responses of subjects to a questionnaire. The IRT models supported are the logistic model, the nominal response model, the graded response model, and smoothing by penalization and kernel. The project also hosts rirt, a package for the R Project for Statistical Computing, and eirt, an add-in for Excel.

BigAl is a platform independent program for calculating really big numbers. It supports not only standard arithmetic, but also calculations with numbers stored in files, exact period determination, continued calculation with predefined factorials, fibonacci with customized seeds, lucas, factorization, ackermann, nth root, random number generation, and more.

Peklo is a graph editor and an environment for visualizing and comparing different algorithms for some graph theoretic problems. Currently implemented are algorithms for maximum flows (including multi-commodity and balanced flows), minimum cuts, shortest path, minimum spanning tree, and maximum matching.