NetLogo is freely available to download from the Center for Connected Learning at Northwestern University. Installation is straightforward, and the software comes with extensive documentation. We recommend that you install the most recent version available.
The original release of the models was compatible with NetLogo 5.x, and those are generally the files linked from individual model pages on this site. They may require in some cases the gradient extension, and the R-NetLogo extension.
More recently, NetLogo has been updated to version 6.x. Versions of the models compatible with NetLogo 6 are available at this github repository.