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.
A music player / organizer. Light as Winamp, useful as iTunes, but music is grouped by albums, and displayed in 3D. Uses Winamp plugins, so can play any music format Winamp can. Has a database which enables quick searching, and quick startup time.