comp.*
Usenet's computing hierarchy — home to languages, operating systems and hardware, and the place where a fair amount of today's software was first announced.
When the Great Renaming of 1986–87 broke up the flat net.* namespace, everything about computers went under comp. It became the largest of the serious hierarchies, with groups like comp.lang.c, comp.unix.questions, comp.arch and comp.os.minix. That last one is where Linus Torvalds mentioned in August 1991 that he was writing a free operating system, "just a hobby", and where Andrew Tanenbaum declared Linux obsolete six months later.
comp.* was also the heartland of FAQ culture. The comp.lang.c FAQ, maintained by Steve Summit, answered the same questions about pointers and arrays year after year and is still cited today. Asking something already covered in the FAQ reliably earned three replies, two of them rude.