You might have noticed that I deliberately split up OpenBSD and FreeBSD in this chapter, but they're just different distributions of "BSD", right?
Wrong.
Unlike Linux, the different "flavors" of BSD don't share a kernel, and are more like different OSes than different distributions.
OpenBSD, FreeBSD, NetBSD, and Dragonfly BSD are all unique and distinct projects.
NetBSD even has a Dreamcast port. Finally, that console has a use!
That's not to say there's no sharing of code and fixes between the distributions—providing porting is quicker than writing your own implementation, and the BSDs are more likely to use more "liberal" open source licenses, such as the MIT license, instead of "restrictive" open source licenses like the GPL (generally for ideological reasons).
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