For details see project website: https://mzattera.github.io/b2fJ/

bin
  Here there are all batch files and executables needed to compile and run Java code.

build
  Temporary folder for builds.

lib
  Libraries; these are built from java sources in src folder.

redistr
  Software used by this project (see COPRIGHT.txt)

src
  Sources for the JVM, standard Java libraries & jtools (TinyVM linker).