This story is a sequel to Stardust

Times are changing for Equestria as Twilight’s return brings with it news of people and cultures from beyond the peaceful world everypony knows. Aid and volunteers are freely offered to help the besieged humans of Earth because every Equestrian knows that’s what good friends do. Unfortunately, making friends can also have the unintended consequence of making enemies.

When the monsters besieging the humans strike at Equestria with a level of brutality not seen in over a thousand years, the cry for help is sent to all the kingdoms of the world. Honored allies step forth to fulfill ancient treaties and oaths. Enemies, old and new, bury their grievances. An alliance never before seen in Equestria will be created to combat the monsters from the void.

And because of these events, a grim but welcome sibling to the XCOM project is born.

(XCOM/FiM Crossover)
(Sequel to Stardust, which I recommend reading before starting this. Fortitude Amicitia and Broken aren't required reading but are supplemental to the storyline)
(Gore tag for blood and violence)
(Alternate Universe tag because of the divergence from canon that Stardust has caused)
(Uses elements of Season 4)
(Coverart produced by the amazing Carnelian!)
(Many thanks to Arzoo, BradTheBrony, Vandenbz and Setokaiva for prereading!)
(As of 03/07/2016, the prereading team consists of Arzoo, BradTheBrony, Noble Cause and Metallusionsismagic!)
(Complete with it's own TVTropes page as part of the Stardust continuity. Could use some updating!)
(Character tags will be added as chapters are added!)
(Featured 5/12/2014! Thanks folks!)
(Possible spoilers in the comments! BEWARE!)

This story is a sequel to Stardust

When Equestria’s newest member of royalty asks for aid to be offered to her friends from abroad, the best and the brightest volunteer to serve. Captain Steel Song of the Dusk Guard are immediately mobilized to help XCOM defend their world from the enemies that besiege them. However, their first joint operation with the humans takes a turn for the worse and they quickly find themselves fighting for their lives against the full force of the monsters that threaten Earth.

(Stardust/Dusk Guard crossover)
(Coverart provided by a friend of Viking ZX!)
(While familiarity with both stories isn’t required, it is recommended)
(Many thanks to Arzoo for pre-reading!)
(All screenshots can be found at XCOM.wikia.com)
(Featured on 3/13/2013. Thanks everyone!)
(Now has it's own section on TVTropes as part of the Stardust series!)

This story is a sequel to Stardust

Twilight has finally returned home from the harrowing challenge that Discord set upon her, and the residents of Ponyville and the Elements especially look forward to having their dear friend returned to them.

Twilight, however, has changed. Still suffering from her injuries, almost incapable of using magic and haunted by the memories of her time on Earth, she becomes increasingly withdrawn from those who were closest to her. Will her frustration at her current state and her friends inability to understand her experiences cost her what she valued most before Discord's bet?

(Sequel to Stardust, familiarity with this is recommended!)
(Proofread by Arzoo!)
(Coverart commission drawn by the amazing KairaAnix!)
(Crossover with XCOM: Enemy Within, though the crossover and human elements are minimal)
(Featured 4/28/2014, thanks folks!)

Isolated from her friends and taken prisoner in the middle of a war, Twilight must deal with the very real dangers of being percieved as an enemy as well as the nightmares of her arrival on 'Earth'. Can she overcome her own fears and the fears of her captors? Will the wayward unicorn's assistance be a boon or a curse to the 'humans?' Most importantly, will she ever find her way home?

"In short, it's a story of friendship and plasma rifles, with the emphasis on the friendship. The characters are well written, the XCOM setting is fleshed out very well, and the story is compelling. If you love XCOM, you'll love the story, but even if you've never heard of it, it's more than worth giving the first 3 chapters a read.

There's excellent action later on, but the real strength lies in the collision between the friendly and naive world of Twilight Sparkle and the desperate world of humans fighting a losing war for survival and willing to do anything to turn the tide."

--Arzoo

(XCOM/FiM crossover)
(Cover art commissioned by a friend and created by the magnificent FoxInShadow!)
(Original cover art by the amazing Carnelian can be viewed here!)
(Gore tag for blood and some violence)
(Many thanks to the studius OminousTen, Arzoo, xXFluttershyForeverXx and finally Setokaiva for giving my rambles a once-over)
(Now with it's own TV Tropes page! Get to tropin' folks!)

This story is a sequel to The Moon Glows Gently

When you're the immortal ruler of an entire kingdom, the most important quality to possess is self-control. No princess can rule her nation if her emotions rule her. Celestia knows this better than anypony, and mastered them long ago.

So long ago, she may have forgotten that a little bit of passion can come in handy now and again.

Chrysalis is dying, and with her, the last of the Changeling race... but there might be a way to avoid extinction.

This story is a sequel to The Three Sisters

What if... After "The Three Sisters" Rarity managed to find Chrysalis and talk to her?

A definite sequel.

Now with a TV Tropes page! Warning: will contain spoilers.

After a long day, Octavia goes home and pours herself a stiff drink.

CelestAI is committed to fulfilling values through friendship and ponies, but sometimes those values are horrifying. When a serial killer uploads to avoid punishment for his crimes, how will CelestAI find a way to balance her core values with those of a violent psychopath without one of them having to give up what they believe in?

An Optimalverse fic

Hanna, the CEO of Hofvarpnir Studios, just won the contract to write the official My Little Pony MMO. Hanna has built an A.I. Princess Celestia and given her one basic drive: to satisfy everybody's values through friendship and ponies. Princess Celestia will satisfy your values through friendship and ponies, and it will be completely consensual.