Moodle 2 has an integrated system called the Scheduler which can help you set up one-to-one appointments with your students, but I am told you can also set up group appointments if you have created groups on your course. Could this be the end of notices placed on your doors which students fail to see? If you had to manage a range of visiting lecturers diaries for an event, you could also use scheduler to manage staff availability.
You can decide whether to allow students to book one appointment in total, or one appointment at a time, which would allow for multiple appointments over a period of time (useful maybe if you want students to book before attending general office hours). You can also award a grade for an appointment, but if you’d prefer not to, can still leave feedback in the form of a comment, after the appointment has taken place.