XStar is a Unix program that simulates the movement of stars. It starts by putting a bunch of stars on the screen, and then it lets the inter-body gravitational forces move the stars around. The result is a lot of neat wandering paths, as the stars interact and collide.
Figuring out what paths these stars should take is called the "N-Body Problem", and when there are more than 3 stars involved (N>3), this can be a very hard problem to solve. XStar is just a "toy" N-body solver, but it generates a lot of pretty pictures and gives you an idea of how stars interact. "Real" N-body solvers have to work with many thousands, or even millions of stars, while XStar works with dozens.
The NRAO Astronomical Image Processing System (AIPS) is a software package for interactive (and, optionally, batch) calibration and editing of radio interferometric data and for the calibration, construction, display and analysis of astronomical images made from those data using Fourier synthesis methods. Design and development of the package began in Charlottesville, Virginia in 1978. It presently consists of over 4300 files containing 1.46 million lines of text. These comprise over 400,000 lines of documentation and on-line help in over 1300 files, and almost a million lines of text in over 2300 Fortran and C source files. It contains over 350 distinct applications "tasks," representing well over 60 person-years of effort since 1978.
AIPS++ is the Astronomical Information Processing System. [It was developed by] a Consortium of radio observatories. About 40 people in all contributed to the first release in 1999. The design was based on object-oriented techniques, and the implementation was in C++ and a glue language called Glish.
A telescope requires post-processing software for calibration, editing, image formation, image enhancement, and analysis of images and other data streams. This software is an integral part of the radio telescope engineering. The Astronomical Information Processing System (AIPS++) project is designed to produce such a software product.
Although AIPS++ is primarily targeted at radio astronomy, it is anticipated that it will also be used in other branches of astronomy and for other applications in image processing and data analysis.
How is it related to AIPS? AIPS++ is the next generation. Little is in common with AIPS, besides some of the algorithms. Data structures, command language, algorithms, user interfaces, applicability have all been substantially improved relative to AIPS.
ODE is a free, industrial quality library for simulating articulated rigid body dynamics - for example ground vehicles, legged creatures, and moving objects in VR environments. It is fast, flexible, robust and platform independent, with advanced joints, contact with friction, and built-in collision detection.