UNDERTRADE is the placeholder title of the genderbent version of the Undertale video game. Artwork was first released at Deviantart on March 24, 2016.
The series is not called "UNDERTRADE" and tends to call itself "genderbent Undertale". There are no real differences in the story, but there are some in the characters.
Characters
Frisk

Frisk (2016).
Since the original Frisk is considered genderless in the sense it's up to the player to decide, the name stays the same.
There are no noticeable differences given to Frisk, except that the colours of their clothes have been inverted.
Chara

Chara (2016).
Since the original Chara is considered genderless in the sense it's up to the player to decide, the name stays the same.
There are no noticeable differences given to Chara, except that the colour of their shirt has been inverted.
Flowa

Flowa (2016).
The female Flowey.
Not much has been changed compared to the original, except for the addition of eyelashes in her design and her more obvious romantic interest in Chara.
Tutoria

Tutoria (2016).
The female Asriel.
Tutoria looks like a small version of Toriel. She wears a sleeveless, green and yellow striped shirt, and black, short skinny jeans.
Unlike Asriel, who received the first part of Asgore's name, Tutoria received her father's full name, followed by the last part of her mother's.
Tuto

Tuto (2016).
The male Toriel.
His hair and horns are similar to Asriel's "God of Hyperdeath" appearance. He wears a purple robe, like Toriel's, and a white cape.
Tuto's name also refers back to the word "tutoriel".
Asgloria

Asgloria (2016).
The female Asgore.
Asgloria has small horns, blonde hair that's long at the back, wears a combination of black and golden armor, a golden crown, a purple wide-sleeved top, purple battle skirt, and a purple cape.
Pristina

Pristina (2016).
The female Papyrus.
Pristina wears a pink scarf around her head, long pink gloves, a white bodycase, a short blue skirt and long pink boots. She has sloppy red lipstick where her lips would be and her nose hole is Papyrus' upside down, and coincidentally shaped like a heart.
She acts- and is dressed like a cliché female anime superhero, and still strives to become part of the Royal Guard.
Like her name suggests, she speaks in the font "Pristina", all CAPS.
Curlz

Curlz (2016).
The female Sans.
Curlz wears black tight shorts, white sneakers, a white muscle shirt, and a light-blue jacket with a white-greyish hoodie she tends to cover her head with at all times. The holes of her eyes are shaped like she has eyelashes, she has a smaller nose hole, and a crack in her skull that ends in a curl.
She has especially wide leg bones, creating the illusion that Curlz has hips, despite being a skeleton.
Like her name suggests, she speaks in the font "Curlz".
Undean

Undean (2016).
The male Undyne.
He looks similar to Undyne, but has a shorter, spiky ponytail, a sharp nail sticking out both elbows, black eyelids opposed to red, wears a short sleeved shirt, and boots without an edge.
Alpheus

Alpheus (2016).
The male Alphys.
He looks similar to Alphys, but has the spikes on his head stand up.
Mathilton
The female Mettaton.
Mathilton has very long hair and a slender body. While she tries to be a charming eye candy for her audience, she is a tomboy in reality, making it seem like her body doesn't fit the real her.
Trivia
- The name "UNDERTRADE" refers to the characters having swapped/traded their nether region. Life isn't that difficult.