Please excuse the WAY off topic post; I'm just so excited.

I love bargain hunting and this is my best purchase yet. We purchased the original platform and equipment (left most) on Craig's List a while ago for $200 ("get it out of my yard, I'm trying to sell my house"). We received the new platform / slide / monkey bars (right) from a friend for $0 this summer ("get it out of my yard, my kids are grown"). Over the last year or so I've sunk another $200 in new hardware. For a total investment of $400, my kids have a $4,000 play set!

Very cool! Though wouldn't it be better with a trebuchet too? 
My thoughts exactly. I've built a working scale model, but I see no way to make it "kid safe".

where r the turrets? the tunnels? the portcalis? hehehe
The two tall posts (right) will anchor the turrets (currently unfinished). The portcullis / gatehouse will be located next to the tornado slide (currently unfinished). The tunnel idea was given up in favor of the swinging bridge (middle).
And the nerf ballista? 
Great idea. There has to be something like that commercially available!