Xplanets is a simulator that shows a spaceship moving through the solar system. The spaceship's movements are influenced by gravity from the sun and the planets according to Newton's laws, and by the acceleration that the engines provide. The planets move around is (simplified) round orbits.
Flan is a network simulator written in Java. It is meant to be easily expandable by adding new protocols, which are also written in Java. It includes a graphical network construction interface, a RIPv2 (with subnets, that is) protocol, IP packets handling, etc. Flan is based on a continuous time-discrete event simulation engine (with real-time sync).
QGolf was developed for radio amateurs to clarify the behaviour of a signal on an antenna. It demonstrates the forces that act on a rope if you move one end of it: you can see how waves are reflected, how resonance occurs, and how multiple pulses coexist on the same rope. Various parameters can be updated during the simulation.
Planets is a fun, interactive program for many-body gravity simulations. The emphasis is on play: it's easy to add in planets, zoom in and out, change the physical constants, save and load configurations, etc. It's designed to be easy enough for a kid to enjoy, but that hardly precludes adults.
SIMPLE_1 (SIMulation Program for Logistics Engin'g) is a discrete/continuous network-oriented simulation language with general-purpose programming language features. The Linux version of this software includes a project management system to automate integration of user-developed C/C++ code into SIMPLE_1 network models. A user's C/C++ code is interfaced with the SIMPLE_1 modeling language through information embedded in comments in the user's header file(s). SIMPLE_1 produces executable files with the help of the C++ compiler.