RootReader2D is downloaded as a jar file (e.g., RootReader2Dv4_3.jar). This file contains everything that you will need to run the program.
RootReader2D requires that your computer have Java SE 8, which is available for a free download from Oracle here. You can test which version of Java you are running here. This software has been compiled to work on BOTH WINDOWS and MAC operating systems.
To launch RootReader2D simply double click on the jar file RootReader2Dv4_3.jar.
java -jar RootReader2Dv4_3.jar from the command line within the download directory.