Graphics engines

Best engine for a huge scale 2-D rts+rpg-type game?

Here's a question, does any 3d accelerated application support multiple fullscreen windows? Also, can I draw two screen buffers into different windows, or would it almost be easier to have one main window, and the second window just read from a 3d buffer to a software buffer then draw that, since although you can't open multiple contexts you can draw to offscreen buffers?