Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
There are lots of different tools for managing your time: Mozilla has a standalone solution: Sunbird and another one based on Thunderbird: Lighting, KDE has Korganizer, and Gnome has the young gnome-agenda and the very popular Evolution, and we must not forget the most famous web based tool: Google Calendar.
All these applications are based on a graphical user interface, and use either iCalendar or the older vCalendar as the data formats.
What about people who prefer console based interfaces and want to edit the data with their favourite text editors? The best solution is remind: it uses an easy but powerful language for describing events. A simple example, this event happens every Tuesday at 13:00 and lasts one hour: