[Complete! With TVTropes apparently!]
Also, apparently, an animated trailer.

In a world of brass and steam, Twilight Sparkle had thought she had made a life-changing discovery with the invention of the telescope. For better or worse, she was correct.

Now her discovery has not only changed her life, but the lives of those she seeks out in her desperate attempt to contact the only other creature as lonely as Twilight herself.

It all would have been much simpler, but it had to be the one Twilight could only call The Mare on the Moon.

Decidedly not within walking distance, then.

[Featured on EQD before story was meant to be submitted. 4/03/2015]

[Editing team: Southpaw, Wolfvenom, Maskedferret, SwanSong and BluePaladin42, without whom this story would be a fraction of its current state.]
[Special thanks to Novel-Idea for the updated cover]

It is the year 2038, and the Earth is slowly being consumed by a space-borne monstrosity dubbed the Black Tide, which is using nanotechnology to remake the planet into something hideously alien.

Erin Olsen works for Project Harmonics, humanity's last-ditch effort to find a new world before the Tide can wipe them out. But when that world is found, and it turns out to be occupied, Erin will need to find the courage to face the unknown in order to save the inhabitants of both worlds.

(Many thanks to Easteu for the fantastic cover image for this story!)

Now with its own TV Tropes page

There is now a follow-up to this story: Sunflower - Side Projects
Sequel: Project Sunflower: Harmony

Celestia and Luna were born as unassuming foals in troubled times. But already marked for greatness, the simple earth ponies stand to face a world set against them, full of danger, fear, and sadness. A world they will change forever.

A sweeping epic taking place before Equestria was made, where Celestia and Luna must rise from normal foals to become the Princesses we know them as, beset from all sides by monsters, other ponies, and even the forces that govern nature. Their tale is as tragic as it is triumphant.

Currently on hiatus. For more info, go here.

(Cover and internal art by Madmax)
(Editing credit predominantly Lightside Luc)

Twilight and her friends are approached by Princess Luna who presents them with a set of questions that trigger a long and perilous journey.

Did you ever stop to wonder what became of Trixie, Gilda and Blueblood after your encounters? What did these episodes truly mean to you? What role will they yet play in the lives of the Elements of Harmony?

Last, are these questions as relevant as the journey towards the answers? Who will benefit from seeking these answers - you, them, or I?

This story is a sequel to Apotheosis

Celestia leaves Equestria in the hooves of Luna and Twilight.

While she searches among the gods to answer her questions, Luna and Twilight must struggle to fulfill their own duties to ponies and to Equestria.
Now with a Spanish translation by SPANIARD KIWI: https://www.deviantart.com/spaniard-kiwi/art/Apoteosis-3-3-857110357

Twilight becomes alicorn of the stars. This is sort of a problem, because Luna kind of already was alicorn of the stars. Oops!

TV Tropes

Celestia leaves to deal with a foreign crisis, giving her sister a chance to rule alone and become more attached to the modern world. She calls on Twilight Sparkle to advise Luna, hoping her student will be able to draw Luna out of her shell. With two major threats to Equestria already defeated in the past year, it seems like the perfect time to let Luna gain some confidence and experience in the modern world. After all, what are the chances of a third disaster occurring?

Now comes with complimentary tropes.

This story is a sequel to The Dresden Fillies: False Masks

It's been a while since the girls have seen their good friend Harry Dresden. Discord escaped, Luna attended her first Nightmare Night, the Royal Wedding was crashed by hordes of changelings, and Pinkie Pie threw a statistically improbable number of parties. They tried inviting Dresden, but between his new job and new apprentice, he always claimed to be too busy. The solution was obvious; if he couldn't come to his friends, they needed to go visit him. Besides, they say Earth is lovely this time of year. What could go wrong?

This story is a sequel to Off The Edge Of The Map

When Twilight is sent with Luna on a diplomatic mission to Draconia, they quickly find themselves somewhere that doesn't appear on any map, and Luna is lost in more than one way...

Thanks to RBDash47 of Pony Fiction Archive for formatting it for submission.
Title image by Valcron

Tremendous thanks to Illya Leonov and Scribbler for the Audiobook version.
Now with a Spanssh translation by SPANIARD KIWI: https://www.deviantart.com/spaniard-kiwi/art/Apoteosis-2-3-857110089

Collected here are the various omakes, bonus chapters and any other extra content from the Dresden Fillies series.

All of the following are non-canon to the Dresden Fillies series, except 'Ditzy Dream' and 'Obsidian Journeys' which are companion pieces to 'The Dresden Fillies: False Masks'. All stories containing spoilers will include a disclaimer.

Story image by Jameson9101322