A stone wall. I'll even draw the sprites for you if I need to.
Something that allows people that do not have access to iron to build them, with mortar, and stones.
Mortar
Mortar should be gainable from using 2 sand with a 7.5l bucket of water, potentially combined with boneglue. To create 10l mortar. (Perhaps 2 clay too?)
Cornerposts
The first block requires, hmm, 1000 stone, 250l mortar? I think that would be quite some grinding for a solo person, I believe it takes 10 seconds to get a stone without a pickaxe, 3 seconds with.
The blocks that follow take 200 stone, 40l mortar. Thats about 3 hours of stonegetting for someone solo without or 50 minutes for someone with. Not even counting the time to get mortar here.
They should take 3x3 or 2x2 spaces instead of the usual 1x1.
Extensions
An extension should take about 40 stone, 10 mortar. Extensions are 2x1.
Gates
Takes about 250 stone and 50l of mortar. A gate should need iron I think, I can't think of any other realistic way to... wait. Drawbridges! They take 20 rope, a load of boards, and perhaps something that resembles a stone nail. About 200 stone nails (more stone grinding, I'm a douche).
Perhaps these bridges should be accompanied by a form of moat to the sides. But...
Moat
...I'm not quite sure, perhaps some way to create moats around the walls that connect to the moat of the bridge, that allows to be filled with 100 liter water per tile (it'll be like a huge container I guess?) Barrels should be allowed to be filled directly from the river instead of using the repetitive bucket thing, it's really unneeded. These moats would stop griefers or force them to swim at a reduced stamina drain rate. Or they need to build a ram-styled structure (needs dried glue before walkable) that allows you to cross moats normally.
Barrel filling
The ability for barrels to fill from rivers and drop into interactable objects without the need for a bucket.
The concept
To allow low-mid tier villages to get a superior form of defense opposed to pallisades. To introduce a form of castles.
Floors, 3d.
Stone walls should be, unlike brick or pallisades, walkable, especially due to their 2x size. This would also introduce some form of 3 dimensions finally in HnH, a long-missing feature we all want. This perhaps might also include the other suggested feature of having a watchtower, as the 3x3 pieces could resemble towers that allow you to scout the area.