You can read it here.

Basically, you can send stuff to an external application that listens to the game. I don't know much about IPC so this is what I got out of articles on forking and stuff.
A demo is included as well as the source code for the external application (written in C#).
If anyone knows how to send data back INTO RM and have RM read it and process it, that might be interesting.
Things that we could potentially do:
-support net capabilities without having to write any of it ourselves
-read and write from excel files or google spreadsheet
-work with databases without having to write our own drivers.
Basically, avoid re-inventing the wheel just for RPG Maker.
Of course, if you want to go mobile or any other platform, this would likely just introduce an extra layer of complications.