is a contact management tool and is a part of Google Apps. Also available as a part of Gmail as well as a standalone service. It stores all your contacts and other details related to them.Google Calendar
is a time-management and scheduling service. It enables you to schedule meetings and events.
To know more about Google Contacts + Vtiger CRM, click here
To know more about Google Calendar + Vtiger CRM, click here
To know more about Google Contacts and Calendar, click here