Bad Manners and Brimstone

I have also seen an email saying something like;

Boss would like to meet with you for one-on-ones.
Please put your name in the desired slot and reply to all.

9:00
10:00
11:00

and then  when Bob gets it and answers first, the next email
says
9:00
10:00 Bob
11:00

and so on.

Or you could use a survey monkey to ask for possible date/ times

or you could just use your email system (e.g., Outlook) and look for open times on the employees calendars and tell them if that doesn't work just to contac tyou.