Lady's bed straw. This plant contains high levels of coumarin, which gives it a beautiful sweet smell somewhat like vanilla or honey. It gets its name because in the past, the plant was often dried and used to stuff mattresses because of its sweet scent.

Therapeutically coumarin has anticoagulant properties, I think some modern medicines like Warfarin are derived from this compound but it's also in some essential oils particularly cassia and cinnamon.
Lady's bedstraw was also traditionally used in cheese making because it contains an enzyme that curdles milk.