Closures
Martin Fowler explains closures, a programming-language construct from the modern LISP/Smalltalk/Ruby school of flexible (and agile) programming.
An odd feature of the craft of software is that, for many of us, languages and development environments got worse in the late 1980's, when the LISP machine era collapsed, and took ten or fifteen years to recover. Back then, a first-rate developer workstation cost about $30K. Now, it's less; development managers hated the idea of a workstation that cost as much as a car.
I'm still not sure why a company would want to take a team of developers, each of whom costs $150K per year, and give them $500 workstations and cubes.