The best way to get emu 3.1 is to go to its
and follow the instructions there. This link should bring you right to the emu-3.1 branch. In order to build in the resulting emu directory, follow the instructions in the README.md file. If using Java, a jar file can be built, a pre-built jar file can be downloaded from this page, or a pre-built jar can be found in java/jars/java8/emu-3.1.jar which was built with Java version 8. A jar built with Java 15 can be found in java/jars/java15/emu-3.1.jar .