Starting with NetLogo version 5.1.0, the use of the Java applets is unfortunately deprecated, as explained here; we plan to move in the future to the NetLogo Web feature, to restart publishing these essays in an interactive way.
So nothing working on line, but it is possible to download the introduction to the Economic Dynamics in a Simple City Model Using Genetic Algorithms simulation work and its .nlogo and .bsearch files (to download, it is better to right click).