Selenio
Selenio helps you manage your reminders in an extremely quick way
When a reminder pops up, you just have to click once in order to choose an action. In case you decide to snooze the alarm, you'll have many predefined options: just choose one and click on it!
Selenio is a cross-platform application: it's written in python and uses the wxPython framework, so it can be used on Linux, Windows and Mac OS/X.
Selenio is an open-source application and is licensed under the terms of of the GNU General Public License Version 2.