Some works of fiction imagine how societies would develop if men and women lived separately.

"You're all off, boys," I insisted. "If there is such a place--and there does seem some foundation for believing it--you'll find it's built on a sort of matriarchal principle, that's all. The men have a separate cult of their own, less socially developed than the women, and make them an annual visit--a sort of wedding call. This is a condition known to have existed--here's just a survival. They've got some peculiarly isolated valley or tableland up there, and their primeval customs have survived. That's all there is to it."
~Herland by Charlotte Perkins Gilman

The anime series Vandread depicts a spacefaring future in which men and women have lived on separate planets for centuries. Now they are forced to cooperate and there is much humor based on the culture shock of the men and women not understanding each other. Most of them still prefer the company of their own sex, but a few are highly intrigued by the opposite and alien sex.

Glory Season
In this futuristic science fiction novel, women are the majority on this matriarchal planet. The founder of the planet's society genetically engineered its inhabitants so that heterosexual intercourse usually triggers parthenogenesis. This novel falls into the "pleasant but stultifying" category of gynotopian speculation. It's also well written and a good read.
"Their aim wasn't to stop science as such, but to prevent a certain kind of scientific fever. A cultural madness, if you will. The sort of epoch in which questioning becomes almost a devotional act. In which all of life's certainties melt, and folk compulsively doubt old ways, heedless of whatever validity those ways once had. Ego and 'personal fulfillment' take precedence over values based on community and tradition."

Eleanor Arnason's A Woman of the Iron People and Ring of Swords
Can be read online at Google Books.
An alien species segregates the sexes because males are so nasty and warlike, while women are peaceful and nurturing. The society is one of the peaceful primitive ones that constantly appear in fiction and never in reality.

In the DC Comics Universe, an immortal species called the Oans separated by sex. The males because the intellectually inclined Guardians, who oversee the Green Lantern Corps, and in time their form changed into very short guys with large brains. The females became the Zamarons, a society of tall, well-built Amazons. After millenia apart, the Guardians and the Zamarons decided they needed to get back together and reproduce for some reason, leading to mating between a lot of short eggheads and tall large-bosomed warrior women in form-fitting armor. Even though I'm a nerd myself, I am still amused by such blatant nerd fanservice.

The Truce by Tanith Lee
I'm spoiling the entire story just by linking to it here. In the distant future, men and women have lived apart for so long that they have forgotten how the species used to reproduce.

The Gate To Women's Country by Sheri S. Tepper
This is a space colony that has lost contact with Earth in which men and women live separately. The women have cooperation and harmony and nurturing while the men are mean old Warriors, though there's not actually anyone else to fight with. Little boys are sent to live with the warriors at the age of five, where the men corrupt them into being horrible violent monsters, which would never happen if they stayed with their mothers. The main characters also spend some time with another society which practices a religion which is an obvious cypher for Christianity. It's equally obvious that the author hates Christianity; the occupants of Holyland, who worship the All-Father, are ignorant and dirty and constantly beat their women and are terrified of the thought of anybody enjoying sex. Oddly enough, no matter how often the enemies of Christianity promote this image of them, real-life Christians stubbornly refuse to start acting the way they are assured they do.

Swastika Night by Katharine Burdekin. In a Nazi future, men and women are kept strictly separated; women are basically breeding animals, kept stupid and degraded, and men who want sex for pleasure or emotional bonding turn to each other. Uplifting, innit.

List of works featuring separatist societies