Programs: calendars

CalDav/CardDav Servers

davical		Most clients seem to be built with this server in mind. haven't set it up.
baikal		Lightweight CALDAV Contacts/Calender server.
radicale		Lightweight CALDAV Contacts/Calendar server
vdirsyncer		like offlineimap for caldav

CalDav/CardDav Clients

GUI
emclient		Mail/Calendar/Contacts (windows only)
korganizer		Contacts/Calendar (unix only)(awesome)
evolution		Mail/Calendar
CLI
khal		CLI Caldav client
WebApp
infocloud		calendar/todos/contacts PHP webapp (creators of caldavzap)
caldavzap		calendar/todos PHP webapp
agendav		calendar/contacts webapp

Tasks Systems

calcurse		cli calendar with notifications and todolist
taskwarrior		CLI task-management system

Other Systems

remind		complex calendar and reminder system
gcalcli		Google Calendar CLI client