Mkmenu is a application menu generator for Fluxbox, JWM and Openbox window managers.
It creates a system-wide menu from all freedesktop.org .desktop files found on the system.
The source code is available for C and Python.
The C version requires the rstring library, which is available here.
Usage:
./mkmenu [—fluxbox | —jwm | —openbox] > OUTPUT_FILE