Horse chestnut tree.

You can make a sort of fuel from it.
But don't.
In the WW2, a method of making a chemical to assist the production of cordite (The explosive used in BIG guns) was invented using conkers.
So, let that idea pass :-)

you could roast them for eating.

NO NO NO!
Do not eat them!
HORSE chestnuts are poison, SWEET Chestnuts are edible.
Different tree.

A toxic substance called aesculin is in the Horsey. To make it safe you would need to boil the things about 6 times, each time with fresh water. To get what? A yellow tasteless mulch that a dog would prefer to roll in than eat.

oops , ive just googled chestnuts and bbc recipe for them... i never knew there was a difference, think the recipe pages on bbc web page should maybe point that out, thanks for letting me know they are poisonous

I think pigs can eat them, but don't quote me!

This was once a school project and the things are can remeber are:
They keeps spiders out of the house. Their bitter taste make it difficult to use as food but with a lime soak they were fed to animals.
They have been used to a make packing cases.
Said to keep aches and pains away if carried in your pocket.