How about a multi-purpose washing line with little humdingers on it so that you can attach certain items to it. One would be an extension to the washing line so as that you can put it higher up, then next would be tightrope cable, another would be bars so you can swing on them, and so on, so you can
change your regular two posts in you back yard into a recreation centre for some of the more endevoring children (and adults!).
Saftey net comes as standard.
This was inspired by my elder cousin Jay, who broke our washing line when I was 3. (it was one of those cross-shaped contraptions that spun around, which was replaced with a two-posted thing after Jay's misadventure.)