Parallel World

In JoJo's Bizarre Adventure, the existence of alternate universes, realities or dimensions is a recurring concept. It is mainly conceptualized as the premise behind certain Stand abilities.

Cream
Vanilla Ice's Stand, Cream is able to devour itself and its user to become a void that devours everything it comes in contact with. Vanilla Ice describes it as a dimension of darkness, though he is unsure himself where exactly the objects are sent to. While in this dimension, Vanilla Ice and his Stand are invulnerable to attacks.

The Hand
Okuyasu Nijimura's The Hand is similar to Cream, able to erase whatever space its right hand touches. Okuyasu states that not even he knows where the voided objects go, but it seems the objects are eliminated like an extremely sharp blade had sliced clean through them. This ability allows the normally short-range Stand extreme distance in its attacks, as it can simply remove the space between itself and a target to bring them within range.

Made in Heaven
Made in Heaven increases the speed or rate of the flow of time; achieved through its ability to control the gravitational forces of the earth, moon, and seemingly the entire universe (in reference to aspects of the theory of relativity).

As time continues to travel, the universe will hit a "vanishing point", and a new universe will be created, where everything repeats itself, according to "fate". Every person in that universe will inherit the memories from the previous one, thus will know exactly what their fate is. They will not be able to change their future, as everything is already written by fate. This is also the idea of Heaven visioned by Enrico Pucci.

In the story, just after Pucci's death at the hands of Emporio Alnino and the Stand Weather Report, the universe is obligated to restart to its original cycle, as the effects of Made in Heaven are now nullified. In this renewed world, characters of seemingly very similar identities to Jolyne, Ermes, Anasui and Weather Report fortuitously gather in Emporio's proximity. However, the characters now have different names such as Irene and Anakiss, along with different lives and memories. This is a consequence of Pucci's death in the hands of Emporio, as now this world's events happened without Pucci being a part of it.

Wired
The hooks and cables stored inside of Pork Pie Hat Kid's mouth are said to go through another dimension when Pork Pie Hat Kid sends them into a bowl of water. The hooks then surge from this dimension into the original dimension through the bottom of a specific object, from example a bird feather or even a beetle.

Dirty Deeds Done Dirt Cheap
President Funny Valentine's Stand D4C allows different parallel worlds/dimensions to co-exist at the same time and/or in the same place. It also allows its user to visit these parallel worlds/dimensions and interact with them. Valentine travels by being closed between two objects, shown first by the use of a door against a wall. This method allows practically anything to travel between dimensions, including other people. Valentine takes advantage of this towards the end of Steel Ball Run to bring forth Diego Brando from a Parallel World to aid him. It is noted that anything that comes in touch with any of its alternate universe counterparts, be it an object or a person, will be destroyed, which applies for both entities. This applies for dead bodies and their alive counterparts, as well. The only exception to this rule is Valentine himself, who can bring other Valentines to this world and interact with them without getting harmed.

Cube House
In JORGE JOESTAR, the 37th universe's incarnation of Reimi Sugimoto is a Stand with an ability named Cube House. Its interior has a tesseract structure and functions as a time traveling device allowing anyone to travel to different universes and time periods. Its primary usage is to take the person using it to go where someone needs their help the most.

Steel Ball Run Universe
The Steel Ball Run universe (SBR universe) is an alternate world within the setting of JoJo's Bizarre Adventure. Its name is derived from the first story set in this new world, Steel Ball Run and also encompasses its successor, JoJolion. There exist a number of names, events, roles, personalities, and relationships appearing in Steel Ball Run and JoJolion similar to those in the original timeline.

Hirohiko Araki indicates in the All Star Battle guidebook that Diamond is Unbreakable and JoJolion are parallel worlds not linked in time or space, and that their respective characters will never meet each other in the manga, including both Josukes and Rohan.

Steel Ball Run
Steel Ball Run, set in 1890, follows Johnny Joestar and Gyro Zeppeli, characters with a number of ostensible similarities to Jonathan Joestar and Will Anthonio Zeppeli. Johnny is learning the Spin, a mystical power comparable to the Ripple, from Gyro, an Italian expert in the art, similar to Will.

JoJolion
JoJolion is set in the year 2011 and follows amnesiac Josuke Higashikata, named after Josuke Higashikata of Diamond is Unbreakable, as he searches for clues to his identity in Morioh, a town named after and located in the same place as the setting of Part 4. Along the way, he discovers ties between himself and Yoshikage Kira, named after the primary antagonist of Part 4.

Trivia

 * Araki conceived the idea of the alternate universe present in Parts 7-8 towards the end of Stone Ocean's serialization, likening the concept of a series returning to its roots to the Italian Renaissance.