UNA Frontiers

Three hundred years after "The Burn," the post-nuke horse-and-buggy age collides with the last secret remnants of the old high-tech world.

The facist Atualphan empire, having annexed most of South and Central America, has conquered the formerly hidden, underwater techno-utopia of New Atlantis. The surviving Neo-Atlantans are under siege - trapped in the unreachable depths of their facility with a year's worth of air.

Two survivors, a boy Noah and Cyberna, an adorable dolphin-shaped AI, must convince the Union of North America to defeat the Atualphans before they become unstoppable with reverse-engineered technology or the Atlantians run out of air.

Can be found here.

Tropes used in UNA Frontiers include:

After the End: Notable for taking place three hundred years later, and for the conspicuous lack of biker gangs.
Atlantis Is Boring: Averted. A population of technically-minded people locked away in a bunker under the ocean floor, all in each other's faces, leads to all kinds of drama.
Berserk Button: Shiratz, just before "The Burn", bolting off and turning his mistress's torturer-killers into mangled heaps of gore.
Beware the Nice Ones: Noah Parks secretly practiced martial arts moves with his homeys, and kills an attacking death-cultist while travelling through the swamp.
Cool Horse. Shiratz and the G.E.M.'S
Divided States of America: Includes the Union of North America, and the New England Maritime Alliance.
Do Androids Dream?: Cyberna gets "visions" now and then, possibly from a neural print of a human woman whose traits were incorporated into her personality. Occasionally, this gets problematic for her.
Eye Scream: Cyberna has recurring visions of a woman with gouged-out eyes, from the memories of another woman whose personality traits were used as her template.
Friendly Playful Doplphin: Cementing human/dolphin ties is what Cyberna originally existed for.
Hair of Gold: Subtly played with here. Dr. Cecille Tremblay, due to the after affects of "The Burn" on North American demographics, is a rare blonde in a sea of brunettes. The section of Quebec where she comes from is considered notable for having a significant percentage of the remaining fair-haired population.
Instant AI, Just Add Water: Cyberna, the New Atlantis's unique, fully-sapient AI.
Lady of War: Lt. Naomi Selbermann is a budding version of this. Col. Sahar Choudhary is the senior officer version.
Lost Technology: PlayStation 2s are a real archeological gem!
Mechanical Horse: The above-named Shiratz is actually a 4,000-year-old alien probe.
Nanomachines: Shiratz can manufacture them internally and literally blow them out his nose for specific purposes. He uses them to create a telepathic link with Noah.
Nuns-N-Rosaries: Cecille is a devout Catholic who walks the walk.
Officer and a Gentleman: Ken Dyson is the quiet, laid-back version of this, but may stray into Beware the Nice Ones territory.
The Empire: The Atualphan empire, a second Incan empire.
Sapient Cetaceans: Cyberna, an AI built in a (mostly) dolphin shape to act as a human/dolphin interface is an example of this. Having spent time with them in their own element, she has few illusions about their actual nature, but she is capable of teaching them "civilized manners" just the same.
Uplifted Animal: The G.E.M.s again.
Schizo-Tech: Horses, radios, airships, and AI's!
The Vamp: Lady Micay.