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.
(When copying straight from the forum: click init before run.)