Google Calender sets the standard for drag-and-drop editing inside of its uncluttered interface. Armed with more than just good looks, rights-assignable group calendaring and integration with GMail's e-mail and contacts databases make it a good choice for the workplace
Zoho Calendar allows to create multiple calendars, share them (with
different access levels), set reminders (by email, RSS), send
invitations, embed public calendars on your site / blog. It has a plugin
for Outlook (for synchronization), mobile version and supports offline
access with Google Gears. Calendars can be synchronized with external
services via ICAL protocol. Zoho Calendar is tightly
integrated to other Zoho services (CRM, Projects, Planner, Mail, Chat).
Centralize knowledge, share documents, have discussions. Keep everyone's schedule online with a color-coded calendar. Post To-dos, Notes, Files, Reminders. Make lists, take notes, share files, email/mobile reminders.
Add multiple to-do lists with date. Mark them completed when they get done. Add email reminders to remind you about your activities. Upload images and files from one place and access from anywhere. Add notes to your page to keep track of your daily activities
Online group task-manager. Allows to create task simply by forwarding email, sending a message from
Facebook or Twitter, or messenger (Gtalk, AIM, Windows Live Messenger,
Yahoo, and ICQ). Through the same channels you can receive task
reminders and notifications. You can view tasks and work with them only
in the web interface, GMail / iGoogle widgets and on iPhone. Soon the
Outlook plugin, Mac and Android-clients will be released.
More than just a calendaring app, Scrybe is a date book on Web 2.0 steroids. It has multiple tools for organizing your life, including to-do lists, a web clipping bookmarklet for grabbing text or images and, of course, a sleek-looking calendar.
ActionThis is a web-based service for managing projects and tasks and making sure they get finished. ActionThis works with your everyday tools to help you get stuff done and go home early.