FORTH
A sourceforge project has built a PDF of Leo Brodie's ancient classic, Thinking FORTH. Thanks, Sunset and Labrea!
FORTH was a remarkable little language of the prehistoric era which traded everything for concision. It had an amazingly tiny footprint -- you could squeeze an operating system, an integrated development environment, and a database application into a memory space smaller than a Web jpeg. In capable hands, it made for elegant programming on very small machines, and it's still relevant for embedded devices and for small machines like palmtops where every byte matters.