Fence

Fences are decorative wooden wall blocks added in the Secret Friday update 8. They count as one and a half blocks tall for player collision, and one block tall for all other purposes. They cannot be jumped over from the same level as the fence but can have other blocks placed on top of them. A fence occupies the center space of blocks and automatically connects to one another when another fence is placed next to it. Fences are one of the many blocks that are broken more quickly with a sword, but deals double damage to it.

Standing on top of a fence in multiplayer counts as an illegal move, and can cause players to get stuck.

Despite being made of wood, fences are not flammable (will not disappear due to fire). However, placing fences near lava will result in fire blocks appearing as the lava attempts to burn it.

Stacking


Multiple fences can be stacked on top of each other by creating a wall of blocks one layer shorter than the intended height of the fence and working down. Removing blocks from underneath the fence doesn't cause it to collapse like cacti and doors, so the lower layers of the wall can one-by-one be replaced by fences easily. This allows the players to make thin pillars or chandeliers to seemingly support floating blocks for decoration purposes. Fences are good to keep around the base for mob zoos because the mobs (except spiders) have no way of escaping.

Future Plans
There may be plans to add a gate, which would most likely be placed like a fence, and fit aesthetically with other fence pieces. However, it would act like a door, where you would click it to open it. Doors work fine as a substitution, but they just look goofy between fences. This topic is most recognized at this thread on Getsatisfaction.com, where Notch himself commented saying "Hmmm... Possibly! Why not?"

Zaun