The Calendar invites being sent to the host and client depend on whether the host has integrated Google Calendar or not. Two scenarios could occur.
Scenario 1
If the host has integrated Google Calendar with neetoCal, when a client books a meeting, neetoCal creates an event in the host's Google Calendar. The client is added as a participating member.
If the client is using Gmail, then the event gets automatically added to the client's calendar too (This is done by Google).
Scenario 2
If the host has not integrated Google Calendar, neetoCal sends the email to the client and the host. Along with the Email we send the event. Since the client has not integrated Calendar, we cannot add it to the host's calendar. Similarly, we can't add the event to the client's calendar because we don't have permission to do it. If the client wants to add this event to their calendar, they can do it by clicking the "Add to calendar" link in the email.