The windows installer is an agent, so in other words it is a client 
You only need the windows installer if you want to monitor a windows pc.
The server is the anvil project. All clients/agents make a http get request, meaning they are reporting to the server if they are online or not.
I will edit the text regarding the windows installer - “…shows error”. Windows will prompt that the installer has a unknown publisher. This prompt will disappear when I buy a certificate. But It’s quite expensive.