The Scalos system was a formerly inhabited planetary system in the Alpha Quadrant. It contained six planets, one of which was Scalos, homeworld of the warp-capable Scalosian civilization. Nearby inhabited star systems included the Talar, Galen, Kiley, Gamma Trianguli, Alpha Majoris, and Algol systems.
By 2259, the Federation had established first contact with this system and could visit it freely. That year, the location of this system was labeled on a stellar cartography chart that was seen on the USS Enterprise's ready room viewscreen. The system's symbol had a blue color, indicating that it was affiliated with the United Federation of Planets. (SNW: "Strange New Worlds", "Children of the Comet")
The system's location was labeled in a Federation star chart that was in Fleet Admiral Kirsten Clancy's office at Starfleet Headquarters in 2399 and on the bridge of the USS Titan-A in 2401. The Scalos system was in or near to neutral space. (PIC: "Maps and Legends", "The Next Generation", "Disengage")
This star system was only mentioned in writing.