Calendars
The Calendar modules can be use for displaying upcoming events on a public page, or used privately to display a schedule for registered users.
Calendar Module
While you can create and assign events to categories, there does not seem to be a way to list just the items in a particular category.
Some other "cons" that I have found include:
The calendar has a non-stadard layout. Days run top to bottom while the weeks run left to right. Could take some getting used to.
Adding an "all day" event is a bit tedious. You assign a date with a time of 0:00 for both the start and finish times.
You can't use apostrophe's unles you deliniate them with a \ before them.
Lastly, (and this may be able to be fixed with an edit of the source code), if you put a WYSIWYG section after the calendar, the text flows around the boxes instead of starting after it. You can also get around this by editing the ray HTML and adding <br clear="all" /> to the start of the box text. (as I did with this box here.)
Event Calendar
The Event Calendar module lets you enter in events for a date, specify how many days they last, add details and even provide a link to an outside page.
EvCal
The original module was written by Fratm and is available for download here.