I strongly recommend that if you are, or aspire to be, a Total Task Scheduler, you must pay close attention to the latest software developments.
Here is an article which outlines some of the most popular calendar apps. I think it leaves out a few good possibilities, and it completely ignores all the auto-schedulers. However, if you are a manual scheduler, it could be useful.
Beyond Google Calendar and Apple Calendar: The 18 Best Apps to Manage Your Schedule.