There's many multiple view rendering methods and examples on the forum but I didn't find a complete example of this one yet. Thought I'd post it for ya'll...
It renders 3 different camera perspectives of a scene (a particle system in this case) to one large 2400x600 window which is meant for a Triplehead output. The window has 3 800x600 videoplanes spread over it. Each camera view is rendered to its own videoplane (= monitor out) using to_texture.
This isn't optimized for frame rate yet. There's obvious fps increases and decreases depending on which windows are visible on which monitor.
Comments and improvements appreciated.