A plugin for JOSM that listens for commands on a TCP port (8111).
It can be used to tell JOSM to zoom to an area and download data.
Details are found on the Wiki page,

http://wiki.openstreetmap.org/index.php/JOSM/Plugins/RemoteControl

Initially written by Frederik Ramm <frederik@remote.org>. License:
GPL V2 or later. Incorporates code taken from YWMS plugin by frsantos.