This story is a sequel to The Best of All Possible Worlds

For generations, humanity has dreamed of discovering intelligent life out in the stars. To say that ending that search in downtown Pasadena was a surprise would be an understatement.

Princess Luna had herself a simple mission: Track Twilight Sparkle and her friends through a malfunctioning portal to Earth, and get them out without being noticed. Luna had no desire to establish permanent relations, or even to stay and talk. After all, both princesses were convinced from previous experience that humans were nothing but trouble.

It appears that both parties have much to learn about each other.

Present-day follow-up to "The Best of All Possible Worlds". "Alternate Universe" tag is because it pretty quickly diverges from Season Two continuity.

The royal court of Canterlot welcomes its newest member with open forelegs: the human philosopher Voltaire, from Earth.

On Earth, Voltaire is known as the greatest enemy of tyranny in the history of literature, and a legend in his own mind.

On Equestria, the court betting pool is giving him a week before the Princess banishes him to the Moon.

Note: This story doesn't have sequels per se, but there are a couple of short follow-ups set in the present day ("Parade Coverage" and "Secret Histories"), and a prequel of sorts in "At the Inn of the Prancing Pony".

TV Tropes page.

You know that feeling? You know, the feeling that you get when you realize you've forgotten something that is very, very important? It is 10:32 p.m. on Hearth's Warming Eve, and Twilight Sparkle has just gotten that feeling...

She didn't think. She just jumped through the portal.

Then it closed behind her.

Stuck in the body of a human teenager, Princess Celestia finds herself trapped in the same world as her bitter student. Even as she and Sunset Shimmer both work to adapt to their new environment and bodies, Celestia is faced with an additional challenge: Sunset Shimmer is attempting to become the queen of Canterlot High, and the only way Celestia can fight back is...

...by becoming more popular.

(Book One preread by DrakeyC and Zef.)

Twilight Sparkle takes a moment from her studies at the School for Gifted Unicorns to get a late lunch. Finding herself in a strange part of the school grounds, an apple tree and its odd fruit tempts her appetite.

This story is a sequel to The Cloudsdale Report

  Twilight’s got her nose stuck in a book. Sunset wants to go see the rest of their friends.

  Things snowball from there.

Highlighted in FimFiction's Feature Box from December 19 to December 22, 2016!
Featured on Equestria Daily on Christmas Eve of 2016!

Historian’s Note: Set in the Wavelengths Timeline where the Sonic Rainboom never happened, Tactics of Snowbound Unicorns is a stand-alone tale that occurs about six weeks after the events in the Applications Trilogy.

Cast: Sunset Shimmer, Twilight Sparkle, Princess Celestia, Moon Dancer, Minuette, Cheerilee, Coco Pommel & Coloratura
Co-Starring: Raven & Philomena

Stories set in the Wavelengths Timeline in chronological order:

Origins Arc
The Alchemy of Chemistry
Bards of the Badlands
Grading on a Bell Curve
Habits of the Equestrian Phoenix
How Not To Use Your Royal Prerogative

Applications Arc
The Application of Unified Harmony Magics
Princess Celestia: A Brief History
The Cloudsdale Report

Dreamers Arc
Tactics of Snowbound Unicorns
A Study in Chaos Theory
Teahouses of Saddle Arabia
As the Raven Flies

Cover Design by Amber Spark
Dark Snow Background by Grim-S-Morrison
Christmas Sunset Shimmer by MoHawgo
Double Diamond Cutie Mark by Pixelkitties
Sunset Shimmer Cutie Mark By Millennial Dan
Text, coloring, snowballs and snowball magic aura effects by Amber Spark

Beta Reader & Editor Credits
Ebon Quill - Quest Designer & Worldbuilding Writer on The Manehattan Project
Little Tinker - Master of Systems at Poniverse & Scripting Engineer on The Manehattan Project
Beltorn - Commenter-at-Large on FimFiction
Painted Heart

Special Thanks:
Quill Scratch & Beltorn - For a last-minute tweaks to the synopsis!

Word Count: 3,800 words
Version: 3.5

Immortals are few and far between in Equestria, and they are all known to each other. Two of them are about to get to know each other a little better. Because one has just turned up uninvited in another’s private chambers. Maybe it’s time they had a chat?

This story contains enormous spoilers for season 6, and won’t make a great deal of sense if you haven’t seen that.

Proofread, edited and significantly improved by NaiadSagaIotaOar. Any remaining problems with the story are from where I didn't heed the advice given.

This story is a sequel to Princess Celestia: A Brief History

  When Celestia first laid eyes on Twilight Sparkle, she knew she’d seen her somewhere before. Though she’d managed to hide this from both Sunset and Twilight, after they departed for the evening, Celestia needed to be sure.
  With her trusted aide Raven at her side and a dangerous threat on the horizon, Celestia heads to the offices of the Equestrian Secret Service to investigate her suspicions.
  Because if she’s right, the possibility of eternal night is the least of Equestria’s concerns.

In FimFiction's Feature Box from October 17 to October 21, 2016 with a Hot tag!

Featured on Equestria Daily on October 23, 2016!

Historian’s Note:
In a timeline where the Sonic Rainboom didn’t happen, The Cloudsdale Report occurs directly after the events chronicled in Princess Celestia: A Brief History, which occur the day after The Application of Unified Harmony Magics.

Cast: Princess Celestia, Raven, Philomena, Twilight Sparkle, Sunset Shimmer

Stories set in the Wavelengths Timeline in chronological order:

Origins Arc
The Alchemy of Chemistry
Bards of the Badlands
Grading on a Bell Curve
Habits of the Equestrian Phoenix
How Not To Use Your Royal Prerogative

Applications Arc
The Application of Unified Harmony Magics
Princess Celestia: A Brief History
The Cloudsdale Report

Dreamers Arc
Tactics of Snowbound Unicorns
A Study in Chaos Theory
Teahouses of Saddle Arabia
As the Raven Flies

Cover Design by Amber Spark in Pixelmator
Celestia’s Cutie Mark by BlackGryp0n (Yes, that BlackGryp0n)

Beta Reader Credits
Ebon Quill - Quest Designer on The Manehattan Project
Little Tinker - Master of Systems at Ponyville Live & Scripting Engineer on The Manehattan Project

This story is a sequel to The Application of Unified Harmony Magics

  After the incredibly awkward reunion last night, Sunset is less than eager about her promise to introduce Twilight Sparkle to Princess Celestia. Maybe it would help if Twilight could go more than five minutes without a panic-driven ramble.
  Despite her doubts, Sunset decides to do her best. But between a bowl of ice water, Philomena’s antics and Celestia’s sly smile, Sunset knows this isn’t going to be easy.
  Still, Twilight probably could have handled it better.

Featured as a Sequel on Equestria Daily on October 8, 2016!
Appeared in the FimFiction Featured Box on September 27, 2016!

Historian’s Note: Set in the Wavelengths timeline where the Sonic Rainboom didn’t happen, the events of Princess Celestia: A Brief History occur the day after the story The Applications of Unified Harmony Magics.

Cast: Sunset Shimmer, Twilight Sparkle, Princess Celestia, Minuette & Philomena

Stories set in the Wavelengths Timeline in chronological order:

Origins Arc
The Alchemy of Chemistry
Bards of the Badlands
Grading on a Bell Curve
Habits of the Equestrian Phoenix
How Not To Use Your Royal Prerogative

Applications Arc
The Application of Unified Harmony Magics
Princess Celestia: A Brief History
The Cloudsdale Report

Dreamers Arc
Tactics of Snowbound Unicorns
A Study in Chaos Theory
Teahouses of Saddle Arabia
As the Raven Flies

Cover Credits
Cover Design by Amber Spark using Pixelmator
Princess Celestia Vector by Wrathx79
Princess Celestia's Room by tamalesyatole
Sunset Shimmer Cutie Mark by MillennialDan
MLP Book Vector by SnowedEarth
MLP Magic Aura Vector by AimeeLovesU

Beta Reader Credits
Ebon Quill - Worldbuilding Writer on The Manehattan Project
Little Tinker - Master of Systems at Ponyville Live & Scripting Engineer on The Manehattan Project

Special Thanks
Fahrenheit - For wonderful advice on creating an epic and entertaining synopsis!

This story is a sequel to Bards of the Badlands

  Sunset hates dealing with chaos surges, no matter how amusing Moon Dancer finds them. After a particularly annoying surge while tutoring Moon Dancer in her advanced telekinetic studies, Sunset takes refuge in the teacher’s lounge. Though she was only looking for a cup of scalding hot tea, Sunset finds a pony walking down the same path she once walked, giving her an opportunity she’s never had before…
  To help somepony not out of guilt, but just because it’s the right thing to do.

Featured on Equestria Daily on September 19, 2016!

Historian’s Note: Set in a timeline where the Sonic Rainboom never happened, Bell Curve occurs in Sunset’s second year as an aide for Professor Apple Polish at Celestia’s School for Gifted Unicorns and several years before the events in The Application of Unified Harmony Magics.

Cast: Sunset Shimmer, Cheerilee, Moon Dancer & Professor Crystal Clear with Philomena as herself.

Stories set in the Wavelengths Timeline in chronological order:

Origins Arc
The Alchemy of Chemistry
Bards of the Badlands
Grading on a Bell Curve
Habits of the Equestrian Phoenix
How Not To Use Your Royal Prerogative

Applications Arc
The Application of Unified Harmony Magics
Princess Celestia: A Brief History
The Cloudsdale Report

Dreamers Arc
Tactics of Snowbound Unicorns
A Study in Chaos Theory
Teahouses of Saddle Arabia
As the Raven Flies

Cover Credits
Cover Design by Amber Spark using Pixelmator
Sunset Shimmer Vector by Midnight-St4r
Cheerilee Vector by J-Brony
Sunset Shimmer Cutie Mark by MillennialDan

Editor & Beta Reader Credits
Ebon Quill - Worldbuilding Writer on The Manehattan Project
Little Tinker - Sysadmin at Poniverse
Painted Heart

Special Thanks:
Orbiting Kettle - For some sorely-needed advice on getting something approaching a good synopsis for this tale!