Coccinella is a free and open-source cross-platform communication tool with a built-in whiteboard for improved collaboration with other people.
ChessDB is a free open-source chess database for Windows, Linux, Mac OSX and most UNIX and UNIX-like operating systems. ChessDB is based on code from Scid http://scid.sourceforge.net/ - a project for which there have been no updates for several years. In
8 Kingdoms is a 3D turn-based fantasy strategic game in which players become kings, build their empires and conquer enemy kingdoms.
ChemVisio is software which might be useful for educational purposes (non-organic chemistry, crystallography etc.). It might be a good visualization support for all people who need better illustrations than that you could see in books.
A combination of useful tools for High School classes, including math classes ranging from prealgebra to calculus, and science classes ranging from IPS to AP Physics.