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.
Kuliax is a relatively complete GNU/Linux live distribution developed and optimized for learning, research, and development use, primarily in higher education. It is based on Debian GNU/Linux stable and Debian Live, with backports.org packages. Custom packages include artwork and electronic books.
Marble is a Virtual Globe and World Atlas that you can use to learn more about Earth: you can pan and zoom around, and you can look up places and roads. A mouse click on a place label will provide the respective Wikipedia article. It's also possible to measure distances between locations or watch the current cloud cover. Marble offers different thematic maps: a classroom-style topographic map, a satellite view, street map, earth at night, and temperature and precipitation maps. All maps include a custom map key, so it can also be used as an educational tool for use in classrooms. For educational purposes, you can also change the date and time and watch how the starry sky and the twilight zone on the map change. Marble also features multiple projections: choose between a flat map ("Plate carré"), Mercator, or the globe.
jHepWork (jWork) is an environment for scientific computation, data analysis, and data visualization for scientists, engineers, and students. The program is fully multi-platform (written in Java). Programs can be written in the Java, Jython/Python, and BeanShell scripting languages. Matlab/Octave is supported for symbolic calculations. The program can be used to display data and functions in D and 3D. It comes with a friendly IDE and a code assist.
Ekiga (formely known as GnomeMeeting) is a soft phone, video conferencing, and instant messenger application for use over the Internet. It supports HD sound quality and video up to DVD size and quality. It is interoperable with many other standards compliant software, hardware, and service providers as it uses both of the major telephony standards, SIP and H.323.