ScreenSaverEngine is the Cocoa application that displays screen saver modules at the appropriate times (after so many minutes, when the cursor is in a hot-corner, etc.). It is part of the ScreenSaver system.
If necessary you can run the ScreenSaverEngine from Terminal:
This is useful for running the engine under GDB for easy debugging.
The ScreenSaverEngine supports some special command line flags to aid in debugging:
High Sierra moved the file/folder location: (they also broke the -background flag, on high sierra) Still an active bug as of HighSierra 10.13.4