Booking websites for student consults

Apologies if this has been asked. I've been searching the website to find a comment on a post I read about online scheduling systems.

I'm looking for a free online system that will enable students to book in consultation times for their research papers with me on pre-set timeslots that I arrange. I have 300 students enrolled so would like to avoid the hassle of emails (if at all possible).

I know that doodle offers something like this, but I don't like the fact that doodle allows everyone to see everyone else's timeslot. I would prefer it to be a more private system for the students.

In a question/answer post I read, someone had mentioned a few websites but me being the idiot I am didn't write them down and now can't find them throughout this website.

Does anyone have any good suggestions? I would prefer to avoid the email back and forth while I wait for students to respond as to what time on a particular day suits, so a booking system would be ideal for both me and my teaching assistant.