BRL-CAD is a powerful cross-platform constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing for rendering & geometric analyses, network distributed framebuffer support, image & signal-processing tools.
You can download file releases of BRL-CAD project from List of release files
System Requirements
Operating System: OS Portable (Source code to work with many OS platforms), MacOSX, POSIX (Linux,BSD,Solaris etc..), BSD, FreeBSD, IRIX, Linux, SunOS/Solaris, Windows, Windows NT/2000, Windows XP