I have something useful but nobody has asked for it

That is what Drop or Collect is for. You describe the item, add up to four photographs, and say whether you will drop it off or somebody needs to fetch it. It is not put straight on the public noticeboard: organisations that take item donations hear about it first and can claim it right away, and it only moves to the public board after about two days if none of them have. If you choose drop-off you are never asked for your address at all. If somebody must collect, your address is stored separately from the listing and shown only to the organisation that claims it, and only after the claim.

This one applies to: I want to help.