Smalltalk-80 Application Architecture by Example. Prepared for an advanced class for Tektronix customers.
Tiles connect Faucet to Spout then water flows.
Computers should devote their full attention to serving the needs of their users. This was understood in 1980. But how exactly does one instruct a computer to do so?
The user-centric battle cry rose over Xerox's Palo Alto Research Center throughout the '70s. Smalltalk was one vehicle for that research. By 1981 I had it running on my desk. And I had source code.
Smalltalk source code was amazingly easy to read. I could flip to just about anywhere, start reading, and make sense of what was there. It reveiled its secrets quickly, except for one: how to make an user-centric application.
My answer was Plumbin'.
Plumbin' is a self contained Smalltalk application written for use in a hands-on lab section of an advanced Smalltalk class. Students were asked to read the program and then extend it. Plumbin' is designed to be small enough to read in one sitting while still offering interesting capability.
The name Plumbin' is a take off on Truckin', another educational simulator developed by the Loops group under Lynn Conway at Xerox PARC. Their spelling probably goes back to the Greatfull Dead, Janice Joplin or Robert Crumb. wikipedia 
Jim Besemer has reminded me that an earlier reference to Truckin' is the old, black, blues musician, Blind Boy Fuller, in his song Keep on Truckin' Baby, Truckin' them blues away... wikipedia