Clock is designed to be a beautiful timepiece and alarm clock manager. Clock supports different time zones, and multiple alarms.

It uses the following projects:
https://launchpad.net/ubuntu-geonames
https://launchpad.net/indicator-datetime

Clock app use the alarm api, that one goes to QtOrganizer which again uses evolution as backend. Evolution stores it in ~/.local/share/evolution/tasks/system/tasks.ics as a caldav file.

indicator-datetime reads those files and sets the alarm on the kernel level alarm interface