Just to clarify things: Solaris is not a real-time OS but Sun did have a real-time OS a decade ago. It was called ChorusOS.

Solaris does have real-time scheduling classes, that approach what most people think they need in a RT OS. And it's the same kernel and distribution as regular production/GA Solaris.

The truth is, the demand for a real-time OS is so low, and the number of serious users so tiny, that Chorus died of loneliness. As an act of mercy, Sun released Chorus as opensource: