The Rift Remover is a utility tool added by the Dimensional Doors mod that gives you the ability to remove rifts created either through the use of a Rift Signature or by the natural spawning of rifts in the world.
To use it, throw the item (default key 'Q') or right click on the rift you are attempting to close. It and any nearby rifts will disappear, leaving a puff of smoke, you may remove this puff of smoke by using (default "right mouse button") the rift remover, taking away its durability and the smoke.
The rift remover will be destroyed along with the rifts.
A Rift Remover is used in the crafting of the Rift Blade.
This item can be used to remove raw rifts that spawn in the world. These rifts grow increasingly unstable, can consume the areas around them, and have increasing probabilities of spawning Endermen in the area.
If there is 2 or 3 rifts close together they can grow and merge into a big rift which will eat the surrounding area and also spawn a lot of Enderman, about 2 or 3 a second.