BRL-CAD is a powerful constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, and image and signal-processing tools.
Cactus is a general, modular, parallel environment for solving systems of partial differential equations. The code has been developed over many years by a large international collaboration of numerical relativity and computational science research groups and can be used to provide a portable platform for solving any system of partial differential equations.
CTSim is a Computed Tomography simulator. It simulates the process of obtaining x-ray data around a phantom object. It then uses various reconstruction algorithms for reconstructing the original image. It supports animation of projection and reconstruction processes, 3-dimensional viewing using OpenGL as well as cross platform support using GTK and Win32.
distributed.net is a loosely knit group of computer users from all of the world that is taking up challenges requiring lots of computing power (most notably the RC5, DES, and OGR cracking contests). It is simple to participate in the challenges by downloading and running their client software (which uses idle CPU time to complete its tasks).
EGO is a program to perform molecular dynamics simulations on parallel as well as on sequential computers. Supported parallel machines include the Hitachi SR8000, CRAY-T3E, IBM-SP2, Fujitsu VPP700, Parsytec-CC under PARIX, and inhomogeneous clusters of UNIX workstations under PVM or MPI. EGO also runs sequentially on any decent UNIX workstation, even Windows95/NT PC's (with a GNU-C compiler) can be used.
GNU TeXmacs is a free wysiwyw (what you see is what you want) editing platform with special features for scientists. The software aims to provide a unified and user friendly framework for editing structured documents with different types of content: text, mathematics, graphics, interactive content. TeXmacs can also be used as an interface to many external systems for computer algebra, numerical analysis, and statistics. New presentation styles can be written by the user and new features can be added to the editor using Scheme.
gpsim is a software simulator for Microchip's PIC microcontrollers. It was designed to provide accurate simulation at real-time speeds. Support exists for all three families of PIC's: 12-, 14-, and 16-bit cores. Simulator features like breakpoints (both execution and memory), trace, symbolic debugging, etc. are all supported. Additonally, simulated stimuli like square waves and analog signals are supported or, if you want, you can create your own dynamically loadable modules (like a 7-segment display). gpsim has both a GTK-based GUI and a readline-based CLI.