An extraordinarily stable BSD derivative for i386 PC compatibles, created by the late BSDi, and eventually sold to Wind River Systems. A great deal of code from BSD/OS was shared with the FreeBSD project, which probably has something to do with FreeBSD 5's greatly improved SMP.
Many ISP's were fond of BSD/OS, and source licenses were both available and relatively affordable.
Unfortunately, Wind River Systems is mostly an embedded systems company, and BSD/OS does not appear to fit into their future plans. As of December 31, 2003, they plan to stop selling BSD/OS internet server, with support to end one year afterwards.
A piece of Unix history will die with it.