The Periaktoi was used to rapidly change the backdrop for different scenes. It was prismatic in shape with three different scenes painted on it. It was easily rotated with only a single side ever facing the audience so that the other two could be changed as needed.
2- Ekkyklema
This was the ancient Greek equivalent of our stage wagons. Bits of scenery could be placed on it and rolled out into the audiences view. It was also often used to wheel out dead bodies. It was just a simple piece of broad wood with four wheels attached.
3-Pinakes
Another scenic element, the Pinakes, were large painted panels (sometimes wood, sometimes tapestries) that were placed in the opening of the Greek skene. They were temporary and could easily be changed. They were often used in a semi circle to help represent a person in the water.
4- Mechane
This devise was essentially a 
crane used to magically lift gods (and sometimes mortals) in and out of scenes. I have also found it referenced as the geranos. Both were cranes used to lift gods in and out of the scene.
5-Masks
No show was complete without masks. These two are both of Dionisis. Every character had 
at least one mask. It is presumed to help people seated to far away to make out facial exppressions understand what was going on. Whether the play was a tradgity, comidy or satyer, the charaters all had masks.
