The z-Tree (Zurich Toolbox for Readymade Economic Experiments) is a widely used software for experiments in economics and political science. It is free but requires a license. The Social Science Experimental Laboratory received such license in 2012. Researchers conducting their experiments in SSEL can use different versions of the available software. As ztree web site advises, "The sample treatments are probably the easiest way to learn about the new features of z-Tree." The z-Tree tutorial explains through examples some of the most common experiments while still more codes and samples can be found on the internet. The Center of Experimental Social Science at NYU (CESS) created web pages  that offer additional examples. Researchers may also find useful z-Tree crash instructions generated by Jonathan Rogers.