Some HDBs have cage bins for bulky refuse. This is for trash that will not fit down the chute. Some blocks use this as their unofficial "freecycling" area and will leave out items they think others may want.
Some town councils allow using these cages for disposal of unregulated e-waste ie small appliances like a toaster over or CD player.
It is not meant for very large items like mattresses and furniture. For such items, see the listing for Bulky Disposal Service.