Ability to send the meeting invitation with optional days/times.
Sometimes it is necessary to invite people with two or three options but only one of them should be accepted. All options should be visible at one time in the calendar and the organizer of the meeting should get an overview of the participants feedback (acceptable/perhaps/declined) in a table with a summary how many participants are available for each option to decide the day/time. Different meeting rooms (one for each schedule) should be accepted as well. Once the decision is made, the unused options should be declined automatically.