(covers information from several alternate timelines)
This page contains information regarding Star Trek: Lower Decks, and thus may contain spoilers.
Caitians were attending Starfleet Academy by the early 2250s, and the Caitian homeworld was a Federation member with members on the Federation Council by 2286. (DIS: "Brother"; Star Trek IV: The Voyage Home) Caitians were present on Qualor II in 2381. (LD: "We'll Always Have Tom Paris")
The Caitians exhibited feline features such as short faces, triangular ears, large eyes with vertically slitted pupils, whiskers, fangs, and a tail. Most were entirely covered with fur that could be orange, brown, gray, or black, and which could be solid, multicolored, or patterned. A few Caitians though had a very different, more Human-like appearance. (Star Trek: The Animated Series; Star Trek IV: The Voyage Home; Star Trek Into Darkness; Star Trek: Lower Decks)
When they needed to move quickly, Caitians could switch to quadrupedal locomotion, displaying feline agility and reaction times. They had sharp claws on their hands and feet, which led some to prefer going without footwear. (Star Trek: The Animated Series; LD: "Mugato, Gumato")
Caitians experienced several hormonal cycles. One of these was the need to be intimate once a year, or else their hormones would drive them crazy; this could be alleviated using a libido post. Caitian females had coital hooks as part of their reproductive anatomy. When stressed, Caitians enjoyed being inside boxes. (LD: "No Small Parts", "We'll Always Have Tom Paris")
A list of all appearances of Caitians (excluding the regular appearances of T'Ana):
The name of the species comes from a biography of Lt. M'Ress, published by Lincoln Enterprises in 1974, which claims that the Caitians are related to the Kzinti, and were from Cait. This is corroborated by extensive commentary by Larry Niven, author of most of the Known Space books and virtually the entire Known Space sub-series The Man-Kzin Wars, primarily found in his short story books "N-Space," "Playgrounds of the Mind," and "The Patchwork Man."
From StarTrek.com, "The felinoid Caitians and the warlike Kzinti share common roots in the deep past — as do Vulcans and Romulans. As with the Vulcans and the Romulans, the two groups went their separate ways to develop as two entirely different civilizations. The Caitians are fierce warriors when so called upon, but pride themselves on their accomplishments in arts and philosophy rather than on the martial arts. Natives of Cait tend to be small and sinewy; the females are as delicately dainty as the Siamese or Abyssinian cats of old Earth. Their family units are extremely close."
The Lincoln Enterprises biography of M'Ress similarly expanded on the Caitians, stating that they tended to be small and sinewy, with their females delicately dainty.
M'Ress is also referred to as a Caitian in the audio story "Passage to Moauv".
Set in 2409, the computer game Star Trek Online features the Caitians as a playable species of the Federation faction, which also employs ships of unique Caitian design, e.g., the Atrox Carrier, Shikaris Escort, and Stalker Stealth Fighter. According to their description, Caitians are "known throughout their quadrant for their intelligence, curiosity, loyalty and love of beauty". The game includes several Caitian NPCs, including Enterprise-F Tactical Officer and Security Chief Lieutenant Kyona. It also depicts a species closely related to the Caitians called Ferasans.