Google Form creators can configure notifications that are sent to a Slack #channel or @user whenever a new response is submitted.
Notify your Slack channel when people respond to your Google Form. Slack Notification allows you to configure the message that is sent using elements of the form.
google-form: John Doe has responded to the form (<# of responses> responses so far. <summary link>)
Notifications up to 20 are free. Additional notifications can be purchased from the Add-ons -> Notifications for Slack -> Purchase Additional Notifications menu.