When they began to read the ancient book Twilight and Spike only had the slightest of ideas what it could possibly be about. As the illuminated inks revealed to them an image of Princess Celestia locked in combat with a massive dragon and his sons they realized that the song written upon the aged pages was telling of a long forgotten battle...

... and that the Celestia they know and love is capable of things they dare not imagine.

Inspired by the image "By Celestia's Might" by John Joseco.

SF (canon species only; no humans) Ponies were magically and genetically engineered to be the perfect servitor race. They are powerful, adaptable, intelligent and completely under the control of their creators. A laboratory accident frees one such pony from her mental chains, but how can one mare save herself and the rest of her kind if she doesn't even know she's a slave?
This is not the Equestria you know and these are not your little ponies... not yet, anyway.

Tags: Adventure, Diamond Dogs, Gryphons, NO HUMANS (did I mention that already?)
Other tags: historical, mind control, Clarke's 3rd Law, excessive use of high energy physics, before they were famous.
Detailed review by PaulAsaran.
Cover art by endrome , used with permission.
Russian translation (partial -- 'unofficially' completed in the comments)
A Soot-Covered World, book 1.

The legends told of their return.

For over a decade Equestria has been beset by the dragons. Every year more villages vanish in flames, and the lonely cities stand as our last redoubt. Winter has gripped the world, and our hope is fading.

But the legends tell of another, a light in the darkness. The Dragonborn, a mythic warrior reborn with the power of the Voice, the only one who can stand against the dragons.

But when she appeared, she was not what we were expecting...

Stranded on a hostile, alien world, Twilight Sparkle and Rainbow Dash must depend on one another and a fellow alien castaway if they want to return home to Equestria.(originally published on FFN)

Only fools, madmen, and adventuring parties go into the Malpheggi, the swamp beyond the Everfree Forest. It can be left as an exercise for the reader as to which of these categories Samus Marcus (a Thyatian swordsman, or so he says) and Ivan (his companion in trouble) fall into. When they are rescued by the registered adventuring party, the Elements of Harmony, a grand quest across the D&D world of Mystara begins. Together they face culture shock, international politics, romance, dungeons, and a dragon with a grudge as Marcus learns how to trust his new friends and make up for his past mistakes while the Elements of Harmony try to save Equestria from a threat which proves more... complicated... than they originally thought. Also, pie. And hats. A D&D (Mystara)/MLP Crossover.

Be Awed and Amazed by the tale of Sweetie Belle as she traverses the multiverse in search of her lost mentor and friend, Twilight Sparkle! Will she find her in post-apocalyptic Equestria? Or maybe in a strange world where everypony is the wrong gender? Or even where a Pony claims to be a human? Read as she journeys through very familiar worlds you might have read about... if you dare!

At this point in time all the main worlds to be visited have already been chosen. Thank you all for the suggestions, and I hope you enjoy the surprises!

Here's the official TSC:F Music Intro: The Sweetie Chronicles: Fragments

WDTP: S2/3-CE
You can also visit the TV Tropes Page which has spoilers!

Inspired by the heroics of the mysterious mare known as the Stable Dweller, Silver Storm, a guard of the town of Marefort, decides to go on a daring mission to rescue her captured brother. Of course things rarely go as planned and her attempts at heroism drags her into a tangled web of plots and conspiracies as warring factions vie for control over the last great city: Dise.

Spanish Version translated by Spaniard-Kiwi: https://www.deviantart.com/spaniard-kiwi/art/Fallout-Ecuestria-Heroes-996263393

Hope is the faith of the young. Losing everything she holds dear, Puppysmiles embarks on the adventure of her life to find her mother, her hopes of meeting her again driving her through the horrors of a world not of her making. Too bad the Wastelands doesn't care about hope.

It is the longest day of the year, and something has gone wrong. Canterlot is in ruins, Celestia is an out-of-control god flying west, and it's up to Twilight Sparkle and her friends to save Equestria. But with the Great and Powerful Trixie playing a reckless wild card, do the girls have what it takes to set things right?