Sign Up Genius A website that lets you create online sign up sheets for volunteers. It allows you to assign tasks and responsibilities. This tool helps alleviate overlap or confusion with scheduling. Email and text reminders and also a great feature that this tool offers.
You Can Book Me Is a similar online tool that helps you with scheduling. It does the same thing but it also connects with your Google Calendar. You can embed or share your available times. Great for parent/teacher meetings.
Both tools offer free accounts!