The Eureka Effect is a replacement for the Engineer's default Wrench weapon and is functionally identical in most respects.
However, the Eureka Effect trades the Engineer's capability to pick up and move buildings around the battlefield for the ability to instantly teleport back to the player's spawn room with alt-fire.
This wrench encourages a more "classic" style of play that requires the Engineer to get building placement right on the first try while giving the player the ability to get away from an otherwise fatal situation.
This weapon is part of the Dr. Grordbort's Brainiac Pack set for the Engineer. However, there is no set bonus for wearing all of the pieces of the set at the same time.