Die wohl beste Kalender-Extension ist Calendar Base (cal) von Mario Matzulla. Sie bietet alles, was man für die Darstellung eines Kalenders und den Terminen benötigt, und darüber hinaus noch viele Extras.
Few things are more frustrating than trying to delete a file only to discover your system says it's locked or in use when you know it shouldn't be. The annoying error messages come in several flavors.