Did you know this was possible in vanilla minecraft?:

Dancing armourstand

If you did, you probably also knew its only possible with comands, and if you didnt, well you do now.

ARMourstands to the rescue!

ARMourstands is server side only, and players with or without it on the client will be able to use it when connecting to a server.

Craft up a normal armourstand and place it in the world

Right click it with 2 sticks to add arms

ARMourstands needs a wrench to turn armourstand parts. By default a vanilla lever works, but you can change that in the configs.

Right click a part with a configured wrench item to turn it. Sneak while right clicking to turn it backwards.
Right click into the air while sneaking to switch wrench mode.

Since ARMourstands only poses the vanilla armourstands around, these will persist in their poses if the mod is removed. Someone might find that useful for map making.

Known bugs:

The two sticks that you use for the arms are not returned when the armourstand is destroyed. This is due to a forge bug that has been reported.

Planned features:

Broken Armourstands keep their poses and can be placed somewhere else.

Copying armourstand poses.

Modpack policy:

Feel free to include ARMourstands in your modpack, you dont need to ask.
However, if your pack is intended for public usage, i ask that you reffer back to this page.

FAQ:

Will you backport this to 1.8.x?

Probably not, not because it would be hard, but because 1.9 is the future anyway. If enough people request it, maybe.

What is this useful for?

Glad you asked! i wondered myself, so i made a few examples: http://imgur.com/a/9UHID

You spelled armor wrong!

No i didnt, you did.