Not sure what specifics you are looking for, but relay's are used extensively from power control to the outputs driven by the M-codes in a CNC program, these also control the solenoids which can be either Hydraulic or pneumatic.
The preference for solenoids is to use DC, they tend to last longer than their AC counterparts which tend to burn out or cause circuit damage if the armature does not shift or is pushed over manually by maintenance personnel etc..
The application are numerous from tool changers to automatic pallet loading.
Al.