For me the most amazing thing about the UNIX tradition is that UNIX was basically written by one guy - Ken Thompson while at Bell Labs. There is a fascinating account of this that can be found here: http://www.bell-labs.com/history/unix/
Some of the quotes are just priceless:
"I allocated a week each to the operating system, the shell, the editor, and the assembler to reproduce itself...", Thompson explained.
Another innovation of UNIX was the development of pipes, which gave programmers the ability to string together a number of processes for a specific output.
It wasn't easy. "It's very easy to say 'cat into grep into...,' or 'who into cat into grep,'" McIlroy explained. "But there are all these side parameters that these commands have; they just don't have input and output arguments, but they have all these options."
Although stymied, McIlroy didn't drop the idea. "And over a period from 1970 to 1972, I'd from time to time say, 'How about making something like this?', and I'd put up another proposal, another proposal, another proposal. And one day I came up with a syntax for the shell that went along with the piping, and Ken said, 'I'm going to do it!'"
"He was tired of hearing this stuff," McIlroy explained. "He didn't do exactly what I had proposed for the pipe system call. He invented a slightly better one that finally got changed once more to what we have today. He did use my clumsy syntax."
"Thompson saw that file arguments weren't going to fit with this scheme of things and he went in and changed all those programs in the same night. I don't know how...and the next morning we had this orgy of one-liners."
"He put pipes into UNIX, he put this notation into shell, all in one night," McElroy said in wonder.
As technically neat as the accomplishment was, when Thompson created pipes, he also put something else into UNIX -- a philosophy.
As McIlroy described it, "the philosophy that everyone started to put forth was 'Write programs that do one thing and do it well. Write programs to work together. Write programs that handle text streams, because that is a universal interface.'"