Space People

The crews of the starships are funny that way
When they're not on a deck they do not like things quiet
They'll turn first a glass then a whole tavern over
Get thrown in the lockup, confined to the field,
And then, in a rush of filled forms and paid prices,
They exit, all quickly, with nothing to say

—Sestina: Midnight stations, GURPS Traveller Starports

In most Space Opera settings space travel is commonplace and routine, but in some settings there are people who spend almost their entire lives in space. These people were born and raised on a starship or space station and can't imagine living on a planet. Often they act as traders, with an extended family owning and operating a ship. Recently, with knowledge of the ill effects of extended periods in space, Spacers are increasingly portrayed as genetically engineered subspecies that do not experience muscular and skeletal degeneration from zero-gravity, are immune to radiation, have prehensile toes...

Compare Generation Ship, where multiple generations are born and live out their entire lives on board a slow-moving ship headed for a distant planet.

Examples of Space People include:

Anime and Manga

The Abh of Crest of the Stars are a genetically engineered race, with key modifications being a third eye to better navigate in three dimensions and the ability to withstand high acceleration and microgravity.

Fan Works

The Freespacers from the Fanfic epic Undocumented Features.

Film

In Serenity Kaylee refers to their ship as their home. They don't really seem to have another.

Literature

C. J. Cherryh's Alliance Union universe has humanity divided culturally into planet-siders, stationers, and spacers. Spacers are usually organized into merchant clans owning one or more ships. They also have one-night stands in ports to prevent inbreeding.
One of Larry Niven's stories features the descendants of stranded astronauts who live in a cloud surrounding a star. They are extremely tall and slim and have elongated toes, as well as a high infant mortality rate due to the lack of gravity.
There are a number of these in the Vorkosigan Saga - notable examples include the Quaddies, who have a second set of arms in place of legs and prefer micro- or zero-gravity environments, and the station-born Elli Quinn, who regards actual planets as dirty and uninviting.
In Isaac Asimov's novella The Martian Way men who make a living from salvaging space junk live mostly in space. Despite having gravity on the spacecraft they still suffer from ill-effects from living in space, such as being scrawny and being expoused to too much U.V radiation.
The "Free Traders" in the Robert A. Heinlein juvenile Citizen of the Galaxy live in nomadic clans whose homes are their starships. They are noted for being somewhat disdainful of planet-dwellers, whom they sometimes refer to as "fraki".

Live-Action TV

Stargate Atlantis has the Travelers, who fled the Wraith in a fleet of starships centuries ago. They did try to start a colony on a planet late in the series, though.
Part of Travis Mayweather's backstory in Star Trek: Enterprise is that he comes from such a family, and thus has a lot more experience in space than most of the crew. Naturally, his family (when they show up) fit as well.

Radio

The titular characters of The Space Gypsy Adventures Radio Drama.

Tabletop Games

GURPS Transhuman Space has the libertarian Duncanites, who invented a parahuman template for life in microgravity. The setting also has a number of groups that live around the Lagrange points in oftentimes-poorly-maintained habitats.
In Eclipse Phase the majority of transhumanity lives in space habitats following The Fall (though there are significant populations on Mars, Venus, and the moons of Jupiter and Saturn). In addition one faction, the Scum, live on converted colony ships.
In Traveller there are a number of people like this including one human minor race. Free Traders are implied to often live like this. And while not the same thing there are a large number of people who while living on planet have more connection to intersteller life then their homeworld.
- Traveller assumes Artificial Gravity and other high-tech perks. The chief annoyance would be the crowding and the closed space; a traveller starship would be no more uncomfortable then a ship on the ocean.
Warhammer 40,000 Roleplay series lists "Void Born" as one of origin world types. A ship roughly equals a city - with its own traditions and usually inhabited by clans with hereditary jobs, since "small" transports and destroyers have crews of 15-20 thousands, a Grand Cruiser around 120-140 thousands. A common Space Station has crew around 10000, but total population (mostly civilian) up to ten times greater, and there are much larger ones.
Stars Without Number Original Edition has Culture/Spacer skill usually coming from background, that sometimes is allowed as a substitute for basic shipboard skills. Also, the Scavenger Fleets are basically space nomads, adapted to living like this (which includes using "shore leaves" to, uh, refresh the gene pool a little) and dealing with the backward planets.

Video Games

In Mass Effect this is one of your possible backgrounds. There are also the Quarians who live entirely on ships and have weakened immune systems (such that they need to wear isolation suits) as a result.
Male Morrigi in Sword of the Stars spend their entire lives after the age of three in space, only "descending" upon a planet to trade or mate. Probably accounts partially for the size difference between males and the planet-bound females.

Web Comics

The Gatekeepers of Schlock Mercenary are aliens who have, as a result of 100,000 years of genetic engineering, more limbs than can be easily counted and the ability to survive vacuum for short periods.
- According to the extra materials (such as Planet Mercenary RPG) the Fobott'r for the last eleven centuries are divided to two groups. One is those remaining on their homeworld, the other are soldier caste mercenaries - there were billions of them by the time their kin... forcibly renegotiated their old beads-and-mirrors deals, and they were stranded, so their descendants became spaceship-based nomadic clans when not hired somewhere else.
In Freefall Winston Thurmad has spacer genes and his parents live in an asteroid, but until the storyline that ran in mid-2020 he himself hadn't been in space since the colony ship from home.

Web Original

Orion's Arm has Space Adapted People, Vacuum Adapted People (for short periods), and Sailors of the Ebon Seas.
Void Dogs has "space gypsies" as well as a parahuman whose feet are more like hands.
While Chakona Space‍'‍s best-known race of near-perfect, genetically engineered hermaphrodite centaurs prefer terrestrial environments there are also Starwalker Stellar foxtaurs that are designed to withstand microgravity and survive vacuum for about an hour.
Not really the majority of Fen in the shared world project Fenspace, but they're the ones who got stories written about them.