IceClean is a powerful System Maintenance and Optimization Tool using only UNIX built-in System Tasks to help your Mac stay healty and to keep it running smoothly.
GanttProject is a cross-platform desktop tool for project scheduling and management. It runs on Windows, Linux and MacOSX, it is free and its code is opensource.
Gephi is an interactive visualization and exploration platform for all kinds of networks and complex systems, dynamic and hierarchical graphs. Runs on Windows, Linux and Mac OS X. Gephi is open-source and free.