Calendar Lock PEA - Calendar Lock PEA is an encrypted desktop calendar with a day, week and month view. The shown calendars are never stored unencrypted on your disk, but exist only in the RAM. Platform-independent, Open Source, no installation or registration required.

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Simple Calendar - A simple calendar with events (optional recurring and reminders), week numbers and a customizable...

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

UKs Kalender - This program helps you organizing your dates and tasks and reminds you of upcoming events.

EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.