Remind1 - Save nerves, time and money - send automated appointment reminder messages from the calendar you already use. Google Calendar & Outlook / Office 365 Integration.
TeamLink - TeamLink is one of the leading and sumptuous solutions that is making web and video meetings extremely easy and efficient.
Remindy.me - Never forget anything!
Google Duo - Google's answer to Facetime, high-quality video calling on iOS and Android.
Appointment Reminder - Automated SMS/Voice and Email Reminders.
Around - Find people to hang out with.