The Bynars are shorter in height than most humanoids and have lilac skin and enlarged skulls. Their most definitive characteristic is that they are interconnected with a master computer on Bynaus. (TNG: "11001001")
When a Bynar is born, a surgeon removes the child's parietal lobe and replaces it with a synaptic processor. Doctor Phlox saw the procedure performed when he encountered the Bynars. He likened the Bynar system to, unknown at the time, a benign form of the Borg Collective. (ENT: "Regeneration")
Bynars always work and live in pairs. Because they are so interconnected with the master computer, the Bynars' language and thought patterns have become as close to binary code as is possible. They can speak English, usually finishing each other's sentences. For example:
In the 24th century, Starfleet employed Bynars to perform computer upgrades on their ships. A team of four Bynars was assigned to Starbase 74, under the supervision of Commander Orfil Quinteros. In 2364, those Bynars commandeered the USS Enterprise-D during a computer refit so that its computer could be used to restart their planetary computer, which had been damaged by a supernova in the Beta Magellan system. (TNG: "11001001")
Background information Edit
The Bynars were collaboratively designed by Michael Westmore and Andrew Probert. The coloration of their skin was influenced by Westmore. He later explained, "At that time we had painted everything [alien] every color we could think, but we hadn't used purple yet, and they became my lavender alien race for the week." (Star Trek: The Magazine Volume 2, Issue 12, p. 26) Probert recollected, "I think I was asked to do the Bynars; I was certainly asked to do their equipment [....] I think Michael suggested that their bodies would actually develop toward each other, which would give them a real asymmetrical look to their heads, which was something we hadn't seen before. He liked the ears that I put on them, but he did something different with the hair." (Star Trek: The Magazine Volume 2, Issue 12, p. 49) Small, beeping mechanisms on the sides of the Bynars' heads were made by Westmore's son, Michael Westmore, Jr., and the Bynars themselves were played by petite females. (Star Trek: The Magazine Volume 2, Issue 12, p. 26)
Outside of the canon of Star Trek, a team of Bynars (110 and 111) was assigned to the USS da Vinci in the Star Trek: Starfleet Corps of Engineers series. When 111 was killed, the remaining solo Bynar, 110, became known as Soloman, a regular in that series.
In the novel Quarantine, two Bynar children were on a shuttlecraft of the USS Gandhi, commanded by Lt. Thomas Riker and piloted by Ensign Shelzane, when the shuttle was hijacked by Maquis posing as DMZ refugees.