Easy Online Calendar for Seniors?

[eRondeau]

I'm trying to set-up an online calendar (website) for scheduling caregiver relief breaks for an infirm senior among a dozen elderly friends. It must be self-managing; each friend would take a day a month. I'd like to send each friend the same private link to access the calendar but otherwise it should be completely open (no Logins, User ID's, or Passwords). The calendar would be a monthly view. Ideally each volunteer's name would be on the left sidebar and they could just drag-and-drop their name to the day they want to reserve. I'm not at all concerned about security, it can be open to the world but with a private URL. If you have the URL you have full access and can do everything. No Logins, no User ID's, no Passwords.

Looking for suggestions as to how to best accomplish this. "Team Scheduling" websites are much too complicated and Google Calendar has way too many options. I need simple, simple, simple -- and foolproof for a bunch of 75-year-olds to use.

Any suggestions?

Thanks!