Pnyx is an easy-to-use and entirely web-based tool for preference aggregation that does not require any prior knowledge about social choice theory. The tool is named after a hill in Athens called Pnyx, which was the official meeting place of the Athenian democratic assembly and is therefore known as one of the earliest sites in the creation of democracy. Pnyx is available at pnyx.dss.in.tum.de. Categories and Subject Descriptors H.4.2 [Information Systems Applications]: Types of Systems—Decision Support; J.4 [Social and Behavioral Sciences]: Economics; H.5.3 [Information Interfaces and Presentation]: Group and Organization Interfaces—Collaborative Computing, Computer-supported Cooperative Work Keywords Preference aggregation; collective decision making; social choice theory; voting; web services