Please note: If you already have a Google Calendar then you should check out Google Calendar's Appointment Schedulers first!
On this page you will find links to websites that help you to arrange meetings.
Typically they allow all participants to specify when they are free to meet and thus allow the meeting organiser to pick a day/time that works for everyone.
This can be very useful for students who need to convene outside of class to do group work, or to allow busy teaching staff to find a mutually convenient time to meet.
As each site does roughly the same job it's just personal preference as to which one you use.
Please click on each link to learn more