Pre-universe

The time before time, also called the Dvapara Yuga, was the universe that preceded or was replaced by N-Space.

Description
The most common understanding was that the current universe, which began in the Big Bang, was preceded by another universe with different laws of physics. (TV: The Satan Pit, Secrets of the Stars, AUDIO: Persuasion, PROSE: Millennial Rites) The Sixth Doctor learned about the pre-universe from the Matrix during his time as Lord President, and he described it to Anne Travers:

"Before this universe was created, there was another one. A totally different universe, with alien physical laws. The heavens were green, and the stars looked like... giant doughnuts, to be brutally frank. Very, very different. And, as in this universe, there were people who discovered the deeper mysteries of time and space."

- Sixth Doctor

According to one account, the Seventh Doctor learned from the Carnival Queen that the Time Lords had misinterpreted their knowledge of the pre-universe and, rather than being an actual separate universe, the pre-universe was the state of reality before the Time Lords created the Web of Time (PROSE: Christmas on a Rational Planet) during the anchoring of the thread. (PROSE: The Book of the War) The Kaliyuga did not merely follow the Dvapara Yuga, it replaced it. (PROSE: Dharmayuddha)

Before the Time Lords created the Web of Time, the universe obeyed no laws of physics, and magic was a powerful force. There existed cities with buildings carved from mile-high arches of ivory, with streets made of cobweb and gardens tended by stone men. (PROSE: Christmas on a Rational Planet) Many humans had semi-divine powers: for instance, Arjuna had one thousand arms and was ardently skilled at compressing time, while Nakula and Sahadeva led armies of imaginary hybrid animals made of broken time. The Great Houses' plan for ending the Dvapara Yuga involved starting the Kurukshetra war between the Pandavas and Kauravas. (PROSE: Dharmayuddha) River Song noted a theory that the SporeShips were leftover weapons from the war that wiped out the previous universe. (AUDIO: Signs)

According to the Kotturuh, there had in fact been universes before the current one. (PROSE: The Dawn of the Kotturuh) Luke Smith theorised that the rules of astrology were based on the laws of physics of the previous universe, which is why the Ancient Lights seemed to conform to them despite them contradicting conventional physics. (TV: Secrets of the Stars)

According to the experiences of the Kin, the only thing that existed before the Big Bang created the universe was a particle of space and time smaller than an atom. (PROSE: Nothing O'Clock) The Second Doctor managed to trick the Vist into travelling back before the Time Lords evolved so that they could claim ownership of time before them. They became stuck in the "no time" that existed before Event One and could never escape there. (AUDIO: The Forbidden Time) Sabbath referred to this period of "no time" as Time Zero. (PROSE: Time Zero)

Natives
The Tenth Doctor said that no life could have existed before the universe came into existence. (TV: The Satan Pit) However, many races claimed to be older than the universe itself. (PROSE: All-Consuming Fire, Millennial Rites, Christmas on a Rational Planet, TV: The Satan Pit, AUDIO: Persuasion)

The Kotturuh believed they had been spreading what they saw as the "gift" of mortality in the prior universes. They did the same in the universe during the Dark Times and believed they would do so again in subsequent universes. (PROSE: The Dawn of the Kotturuh)

When the new universe was created, many powerful species from the pre-universe fled into other realities but over time found their way back. Some, like the Great Old Ones, still followed the rules of the pre-universe, giving them god-like powers. On many planets, these beings became part of the legends and religions. (PROSE: All-Consuming Fire, Millennial Rites)

The Beast was trapped under Krop Tor by the Disciples of the Light before light, time, space, or matter existed, and he remained there during and after the creation of the universe. (TV: The Impossible Planet) He claimed to have inspired the Devil of all religions, including the Arkiphets, Quoldonity, Christianity, Pash Pash, New Judaism, San Klah, and the Church of the Tin Vagabond. (TV: The Satan Pit)

To survive in the new universe, some entities survived by rooting themselves in fantasy and faith, becoming gods of different planets. In the Sol system, Gaia aligned with Earth, Ares with Mars, Aphrodite with Venus, Pan with El Mundo, and Hestia with Planet 5. (PROSE: The Rise and Fall of Señor 105)

The Shepherd and Shepherdess escaped the "extinction of their universe" and arrived in N-Space, where they became transparent in appearance. They moved without touching the ground and their hair and nails grew longer because they were dying in the new reality. (AUDIO: Persuasion)

Luke Smith speculated that the Ancient Lights came from before the universe. (TV: Secrets of the Stars)

Jack Harkness said that the Syriath had been trapped within the Rift since before time. (AUDIO: The House of the Dead)

Entropy Sirens were said to have existed before the universe. (AUDIO: The Entropy Composition)

Iris Wildthyme knew that the Lord Temporal of the Clockworks originated from the previous universe but had crossed the rapids between cosmoses to tend their Tale Without Meaning to the exclusion of everything else. Their Wordships each began as single sounds carried over from the pre-universe, amplified and refined, until it became alive and was added to the Tale. (PROSE: First Meetings)

The Dark was said to have been formed from the remains of the void before the Big Bang. (PROSE: Fear of the Dark)

The consciousness called the Solitract existed in this period and was "banished" to the Solitract plane by the physical laws of the universe due to its incompatible energy constitution. Anti-zones formed when the Solitract made contact with the universe. (TV: It Takes You Away)

At the Deadly Boutique, Jessie was transformed into a creature from before time began. Brenda wrote about this "funny do" in her letter to the readers of the books series about herself and Effie, written by Paul Magrs. (PROSE: Brenda's B&B)