Lingvisto is a small X11 program that will help you to learn words from foreign languages. You can create your own lessons and test your knowledge afterwards. Lingvisto supports a variety of languages. If you want to learn a language that contains special characters (or your native language contains such characters) you have to install the corresponding X11-font into your font directory.
Linux Letters and Number is a fun and educational learning game intended for children 2 and up. It helps children learn or improve their letters, numbers, spelling, and vocabulary skills through the use of interesting pictures. It also helps them develop important computer skills too. It is written in C using the GTK and GDK_Imlib libraries.
MathWar is a flashcard math game in which the child plays against the computer to solve simple addition, subtraction, and multiplication problems before the computer player answers. MathWar is aimed at kids who are just learning their math facts, and can easily be tailored to fit different skill levels.
Maxima is a Common Lisp implementation of MIT's Macsyma system for computer based algebra. It features plotting over the network via netmath, computations over the network, extensive testing on a large array of problems, a source level debugger for maxima code, ease of extension in fundamentally new ways, access to Common Lisp and portability to many systems.
NetMath is a web browser which knows something about math. It has built-in plotting engines and the ability to communicate with computation servers. This makes it possible to do local graphics, zooming and panning, while taking advantage of sophisticated computational programs. Documents contain active and editable items, and the results of computations appear in the document.
Astronomy for fun (education, science, whatever). Nightfall is an interactive application to simulate eclipsing binary stars, and to produce animated views, synthetic lightcurves and more. Takes into account the non-spherical shape of close binary stars, mutual reflection, and some other effects. Comes with documentation, on-line help, and lots of observational data of real binary stars. Supports the Gnome desktop, but doesn't require it.