This 'NoSQL' has absolutely no similarity to the 'NoSQL' databases of the last few years (and predates them all by many years). Instead it's a tool to manage databases of plain text files in the Unix environment. Seamlessly ties together several parts of Unix toolchain, with Awk as the centerpiece. Has surprising features, like searches with joins between tables (i.e., files).

I'll also second that the Aho Kernighan Awk book is a beautiful piece of work.