gcalcli

CLI to access Google Calendars; allows to do the main tasks: create, delete, and list events.

khal

CLI and terminal calendar program, able to synchronize with CalDAV servers through vdirsyncer.

pal

Calendar program for Unix/Linux systems that can keep track of events; custom, plain text storage format; interesting and fully functional.

Remind

Calendar program with possibility to set complex rules to define events; custom, powerful text-based storage format.

Wyrd

Curses front-end for Remind written in OCaml with vertically scrollable time table.