You can obtain a 'standalone' installation of the CODESYS Gateway (V3.5) as follows:

Installing via the standard CODESYS setup

• This is the preferred variant, since in this case the gateway – understandably – 'matches' the CODESYS IDE, in addition to which the gateway is registered automatically as a service. To do this, select only the gateway in the setup during the installation:
  
• You can see in the services or by the symbol in the task bar whether the gateway is running (if it was installed via CODESYS):
  

Starting manually from the folder "GatewayPLC"

• Copy the folder *C:\Program Files (x86)\3S CODESYS\GatewayPLC* from an existing CODESYS installation to any desired directory on the computer on which the gateway is to run.
• Create a shortcut to the file GatewayService.exe and add the destination in the properties with the option "-d" (<Path>GatewayPLC\CODESYSControlService.exe -d). The gateway thus starts in debug mode and displays the log outputs. You can also add this shortcut to the Windows start menu.