A type of application software that functions as a personal organizer is called personal information manager (PIM). As an information management tool, a PIM's purpose is to facilitate the recording, tracking, and management of certain types of "personal information" such as personal notes, address books, significant calendar dates, reminders, email, RSS/Atom feeds, voicemail and more.
Here are some of today's best free/open-source Personal Information Managers:
KonsoleKalendar is a command line interface to KDE calendars. It lets you view, insert, remove, or modify calendar events by way of the command line or from a scripting language. Additionally, KonsoleKalendar can export a KDE calendar to a variety of other formats. KonsoleKalendar is intended solely for uses where a graphical user interface is not practical or possible. KonsoleKalendar is part of the KDE PIM package.