EFL stands for Enlightenment Foundation Libraries (
https://www.enlightenment.org/develop/efl/start ). This library is widely used for Embedded GUI applications on resource constrained devices (the sort of devices where the JVM doesn't work well) that run some form of Embedded Linux (Raspberry Pi, Beaglebone Black etc). Think of EFL being somewhat similar to GTK since it is a GUI toolkit. Various backends are supported by EFL including XOrg, Wayland, and the Linux Frame Buffer (many Embedded Linux GUI applications use it for performance reasons). Samsung is the largest user of EFL where they extensively use it in their
Smart devices (watches, TVs, fridges etc). Another major EFL user is Electrolux (
https://www.electrolux.co.nz/ ) where they used the library for an Embedded Linux GUI application on some of their
Smart fridges back in 2010.