GeoGebra is free and multi-platform dynamic mathematics software for learning and teaching geometry, algebra, statistics, and calculus. Download the free software at http://www.geogebra.org. Find the sourcecode at http://www.geogebra.org/trac
VisualPetri is Petri net editor for Windows platform based on GDI Plus library with an integrated simulator. Note: a Petri net is one of several mathematical representations of discrete distributed systems.