A list of alternate realities and spin-offs that were added to the Saint Seiya series over the years:

Canon timeline

The canon timeline, manga timeline, or Kurumadaverse is the original manga timeline created by Masami Kurumada. It includes:

Series Notes and observations
Manga The first work of the series, containing most of the canon material.
Gigantomachia Is an Novel written by Masami Kurumada and Tatsuya Hamasaka.
Episode G Is a official Gaiden of the manga series. Is written and illustrated by Megumu Okada, and supervised by Masami Kurumada (he writes the Original Draft of the story).

Set over 7 years before the Galaxian Wars Arc (with the exception of the prologue, that happens 13 years before the arc), it tells the story of the saints and their holy war against the Titans and their army. It focuses on the 12 gold saints of the 20th century.

Next Dimension The official sequel to the manga series. Is written and illustrated by Masami Kurumada.

It is a prequel and continuation to his manga series Saint Seiya; a part of the story is set in the 20th century(shortly after the holy war between Athena/Saori and Hades), a part is set in the 18th century during the previous holy war between Athena and Hades.

Saintia Shō

Is a official Spin-Off of the manga series. Is written and illustrated by Chimaki Kuori, and supervised by Masami Kurumada (he writes the draft of the story).

The story is developed after the defeat of Gemini Saga (in the Manga), the Sanctuary faces a new threat known as Eris, the Goddess of Discord and Chaos, with her minions, the Dryades. The story is developed in parallel with the Manga.

Anime timeline

The anime timeline, or Toeiverse is the reality created by Toei Animation with the changes and fillers of the Saint Seiya anime series and its related media. It includes:

Series Notes and observations
Anime The animation of the original manga series, which makes many changes to the timeline.
Chapter Sanctuary The first part of the Hades saga's OVA series, released long after the anime.
Chapter Inferno The second part of the Hades saga's OVA series, released long after the anime.
Chapter Elysion The third and final part of the Hades saga's OVA series, released long after the anime.
Toei side stories A collection of short stories that explain events that happened in the anime timeline that differ from their manga counterparts (e.g. the death of Pope Ares, the brainwashing of Capricorn Shura etc.).
Soul of Gold The unofficial sequel to the Hades saga, which tells the fate of the 12 Gold Saints. It follows the anime's fillers (specifically, the Asgard saga).
Omega Another unofficial sequel to the Hades saga, telling the original story of the holy war against Mars and his martians, and the battles of 21st century saints.

Film timeline

The film timeline, or Movieverse is a loosely connected timeline composed by the first four independent movies of the series. They follow the anime timeline to some extent. Virtually all of the films' main antagonists are defeated by Pegasus Seiya, while the saint wears the Sagittarius Cloth.

Series Notes and observations
Evil Goddess Eris The fight against the goddess Eris. Set before the Sanctuary Arc.
Heated Battle of the Gods The fight between saints and the God Warriors. Set before the Sanctuary Arc.
Legend of Crimson Youth The appearance of the god Abel and resurrection of the Gold Saints killed in the Sanctuary during the saints' civil war, set some time after the Sanctuary Arc, and presumably before the Poseidon Arc.
Warriors of the Last Holy War The battle between saints and the Evil Angels of Lucifer. Set after the Poseidon Arc.

Lost Canvas timeline

The Lost Canvas timeline, Shioriverse, or Teshirogiverse is the timeline of the works written and illustrated by Shiori Teshirogi, under the advisement of Masami Kurumada, that act as an alternative prequel to the manga timeline.

Series Notes and observations
The Lost Canvas An unofficial prequel to the series, that tells the story of the previous holy war between the saints of Athena and the specters of Hades, in 1745 (over 241 years before the Galaxian Wars Arc).
Gaiden A series of stories that range in time, acting as both a sequel and a prequel to The Lost Canvas' main story (excluding its epilogue). It focuses on the gold saints.

In Volume 13, Aries Avenir travels back from a completely different timeline, in the far future, as the sole survivor of a holy war where Athena had lost to Hades.

Heaven Chapter timeline

The Heaven Chapter timeline, or Zeus saga timeline is a cancelled timeline, and an alternative to Next Dimension, where the saints were supposed to fight the Olympic deities, and the gold saints' souls have been sealed and imprisoned together in a statue.

Series Notes and observations
Overture The first and (due to the cancellation) last movie in the series, acting as a direct sequel to the Hades saga, where the saints face three Angels and the goddess Artemis. At the final scene, Pegasus Seiya also faces the god Apollo.

Legend of Sanctuary timeline

The Legend of Sanctuary timeline, CG timeline, or Suzukiverse is the timeline created for the film Saint Seiya: Legend of Sanctuary by Toei Animation, written by Tomohiro Suzuki and produced by Yousuke Asama.

Series Notes and observations
Legend of Sanctuary The first and (presumably) last of the CG movies, it loosely depicts the events of the main series in an alternate reality, with different designs.

No timeline

These stories not are part of the manga, anime and spin-offs.

Series Notes and observations
Hypemyth A special story included in the magazine Cosmos Special on the lore of Saint Seiya. The story not was written by Kurumada and has several errors with the manga of Saint Seiya.
The Cygnus Hyoga (Gaiden) A story or gaiden focused on Hyoga. The story was written by Kurumada but is not part of the continuity of the manga.