The HEPREP 2 standard, see heprep.freehep.org is implemented in C++ and Java as part of the FreeHEP library.
The C++ version is in use by GEANT4 and other programs, while the Java version is in use by WIRED versions 3 and 4. The Java version of HepRep also implements a converter to convert HepRep version 1 into HepRep version 2.