FreeBSD
FreeBSD is an operating system derived from Unix and available for free (but you could probably have guessed that). Actually, FreeBSD came out of the “Jolix” (386BSD) operating system, one of the main Berkeley Software Distributions (BSDs). No less than Linus Torvalds himself has praised 386BSD, saying that he might never have created Linux if he’d had access to 386BSD at the time.
By the time of FreeBSD 2.0, at the beginning of 1995, a new package management system and a more optimized virtual memory system. Among the growing number of high-profile users at the time were Hotmail and Yahoo, who benefitted greatly from the advanced networking and security features of the OS, as well as numerous advantages in storage and portability/ compatibility. FreeBSD plays very well with different processor architectures, and various Mac and Linux operating systems.
FreeBSD serves a an exceptional example of open source development, with a number of developers participating in the project for over a quarter of a century. Use and redistribution is governed by a simplified version of the original BSD License, which is approved by the Open Source Initiative and compatible with the General Public License. However, derived works may be included in proprietary, closed-source releases (such as OS X for Mac).
If you are a developer and have either used, or would like to use some of the kernels that derive from this system, be aware of the technical requirements that drive the basic engine. Since there is no cost to the shared system files, and the basic operating bits are open source, this is an excellent starting point for future development taking advantage of the specialized nature of this technology. What keeps the operating system vital and unlikely to be soon obsolete is the elegant simplicity of its core design. Multi or single thread, pre or post packet packaging, and robust basic code make for no-care, long term application maintenance, and reliable tranferability of data to even the most modern systems. Simple translation across Windows, DOS, OS-X, and now Android and iOS will keep FreeBSD in play for many more years.
We recently installed a system in the Hyerbadd Care facility, where many of the patients are responding to medical tourism programs for hip resurfacing. Many other examples of recent application of this existing technology are available from the developers.