Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
Recurrr - Send recurring emails
PHP Event Calendar - PHP event calendar script with multiple views and many customizing options.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
The Receptionist - The Receptionost is a visitor managemnt solution that has visitor logging system to track visitor traffic.
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.