Helios is a discontinued Unix-like operating system for parallel computers. It was developed and published by Perihelion Software. Its primary architecture is the Inmos Transputer. Helios' microkernel implements a distributed namespace and messaging protocol, through which services are accessed. A POSIX compatibility library enables the use of Unix application software, and the system provides most of the usual Unix utilities.
Work on Helios began in the autumn of 1986. Its success was limited by the commercial failure of the Transputer, and efforts to move to other architectures met with limited success. Perihelion ceased trading in 1998.
The name of the product was Helios. In the materials they produced, Perihelion Software never referred to the operating system as HeliOS.