Multi-body Gravity Simulator (MGS) allows you to perform a simulation based on a fixed time slice. Its unique features are the ability to perform realtime simulations, a three dimensional visualization of the simulation, and the ability to design simulations in XML and with a GUI. The accuracy of realtime simulations will depend on your machine speed. Fixed time step simulations are also supported.
Frink is a calculating tool and programming language designed to help you in the real world. It tracks units of measurement throughout all calculations and ensures that answers are correct. It converts between systems of measurement, and has a huge library of physical data. It is both a simple calculator for quick calculations and a full-fledged programming language for large tasks. It draws high-quality graphics, handles conversions between time zones, currencies, and historical values of the U.S. dollar and the British pound, translates between several languages, does date/time math, and more.
McIDAS-Lite is a freely available demo for the full McIDAS software. It will connect to a variety of free online data sources for satellite data and display the images in a viewing window. Images can be looped and analyzed, and graphics overlays can be created to show maps and other geographical features. It is available for AIX, HP-UX, Irix, Linux, Mac OS X, Solaris Sparc, Solaris x86, and Windows XP with SFU.