Calligra is an integrated suite of applications that cover office, creative, and management needs. It offers applications on both desktop computers and mobile platforms like tablets and smartphones. OpenDocument Format (ODF) is used, making it compatible with OpenOffice.org, LibreOffice, and Microsoft Office. Calligra Suite contains the following applications: Calligra Words (word processor), Sheets (spreadsheets), Stage (presentations), Flow (diagrams and flowcharts), Kexi (visual database creator), Braindump (note taking), Plan (project management), Krita (drawing), and Karbon (vector graphics).
Five Hundred is a card game for four players similar to Euchre or Bridge, especially popular in Australia and New Zealand. The wikipedia page has a comprehensive description of gameplay. This version is implemented in C++/Qt. It incorporates graphics from the svg-cards project. Computer players are scriptable in Lua.
Multiple Eyepairs Only is a project to define a file format and to provide tools to use cryptography for things like four-eyes principles. The key idea is this: if information should only be accessible to a group of people together, with the additional possibility to have some redundancy in participants, then MEO is for you.
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.