Tesseract
The Tesseract is an alien artifact in the Marvel Cinematic Universe. In appearance, it is a glowing translucent cube. It is one of six "Infinity Stones"; ancient objects of super-advanced alien technology.
Properties
With the right technology, power can be drawn from the cube in vast amounts. Swiss inventor Arnim Zola was able to use its energy to power everything from directed-energy handguns to strategic bombers and WMDs.
The cube can also be used to open wormholes to distant locations, such as a rift between Earth and Chitauri space.
The cube can apparently also broadcast power to some devices, such as the staff/sceptre that Loki wielded during his attempt to rule the Earth.
Directly handling the Tesseract is unsafe, although it can be done briefly without serious consequences. Johann Schmidt was apparently disintegrated when he held onto the cube for too long.