Commonly known as beefstake fungus, due to the colour and texture of the flesh.
Beefstake fungus causes brown rot, favouring the cellulose in the wood.
I have seen this fungi on oak and sweet chestnut.
Beefstake is an annual and usually decimates in the first frosts, but can sometimes linger longer.
It decays into a blackened state, often with a blueish mould present.