SendLuaRulesMsg is pretty cool sends strings and aint afraid of nothing.Widget to gadget communication, how would one set that up?
An imo relative simple example is in the unit poser:
http://springrts.com/phpbb/viewtopic.php?f=14&t=25104
on the widget side:
tp_buttonsender.lua sends unsynced stuff (button presses on a players keyboard)
via Spring.SendLuaRulesMsg
on the gadget side:
tp_unitmessagetransmit.lua recieves the messages
via gadget:RecvLuaMsg ()