Let me help with some ideas based on having an application used for years as spectacular as DateBK (hhttp: / / www.pimlicosoftware.com/datebk6.htm).

Allow them to stop recurring appointments choose each number of weeks / months that repeats, which days of the week are repeated and for changing a meeting of a specific day and time without losing the whole chain of related appointments. For example: I have classes every Friday at 18pm but the fourth Friday suspends and changes the Thursday of that week at 19pm. Separate this appointment should be allowed without affecting the appointment repetitiba all Fridays at 18pm.

Also:

Allowing repetition task management in time, percent complete this task and when to begin and
finish.

Allow to associate tasks and notes to appointments on the calendar.

Add support to include access to documents, images, etc ... both calendar appointments and tasks and notes.

Do not forget to support keyboard shortcuts.

Thanks.