The slowest of the date modules, but one of the most powerful. Includes support for recurring events and custom calendars. Excellent parsing of English dates and times such as '5PM next friday'. It is also pure Perl, making it easier to install on some platforms than similar modules. If you haven't switched to DateTime, and don't need the speed of Date::Calc, Date::Manip is a powerful and easy to use alternative.
on of the good date manipulation modules around, probably the best. i've been using it in production environments for more than two years and it has prooved to be the best choice. just to mention: the author invented recurrence events scheme, that IMHO turns out to be better by the one used with cron.