SquirrelJME is a Java ME 8 Virtual Machine written purely in Java, which also intends to be compatible with J2ME! If you do not know what J2ME is, it is the Java of old flip phones which run MIDlets. In 2014 a new embedded Java standard was released and this is the standard which SquirrelJME is based on, meaning that it is easier to program and far more modern. This is a work in progress and not every single application will run (currently just basic applications), but support for more applications is coming in the future! Currently it runs on existing Java SE VMs so you will need a Desktop Java SE installed. SquirrelJME will see a port to RetroArch in the future as well, however that is still a few months away.