2025 - Freecycle and similar Free stuff

Since I've no idea what they're like "in the flesh" you'll have to make allowances for my ideas
They could be used as barriers/fences/screens, stood on their sides.
Four on their sides would make a square enclosure ? compost, leaves, a planter. Another one on top is a roof!.
Three on their sides make a triangular enclosure - perhaps round a tree to keep beasts away.
A path in a tunnel or across wet ground. Solid enough for a wheelbarrow?
I really, really want some now.

PS one would be great to put a hotbin on.

I think all your ideas would work.  They would need lining for a raised bed / planter . They are of the larger size pallets you can get.      .
A leaf or grass holding enclosure is a good idea. Some where for it to go before it gets added to the compost. 
Hotbin stand was my very first thought     .
And when they are the right way up they have 9 built in plant pots.