On-Call schedule webapp

I need a simple web solution for planning on-call schedules. Team of 5-8 sysadmins work in a team and are on-call 24/7 by a shared schedule, currently planned by an excel document. Features: Profiles for all team members, Contact details, email + phone numbers + photo. Browsable calender with current month visible, initials on every calender day display what person is on-call. One admin account for updating the schedule is needed The application should be readonly if not logged in. Please provide installation details also.