A popular and free version of the UNIX operating system that runs on x86-compatible, DEC Alpha, PC-98, AMD64, IA64 and SPARC64 architectures. FreeBSD is distributed in executable and source code form. The source code enables ambitious users to actually extend the operating system.
Another popular and free version of UNIX is Linux.
Learn more about Open Source in Webopedia’s “Did You Know…?” section.