CastaCal

show calendar

To use the calendar, register quick and easy, or have a sneak-peek here. Once logged in, the calendar will appear and by just double clicking on a date in any view, you can add your appointments.
Share you calendar with others, by sending them a link to your calendar: In calendar view click on link and copy your link.
Now they can see your entries, and if they register themself, they can add their own private entries.
Note: you stay logged in, until you manually log out.
Assume you have your own calendar and a link to a shared calendar of someone else (example: http://CastaCal.com?cal=A74EF49DBF69E842E85B33104C0D83E9 for the sample calendar)
Then: while you are logged in:
    http://CastaCal.com will bring you to your own calendar.
    http://CastaCal.com?cal=A74EF49DBF69E842E85B33104C0D83E9 will bring you to your combined calendar.
If you are not logged in:
    http://CastaCal.com will bring you to a sample calendar.
    http://CastaCal.com?cal=A74EF49DBF69E842E85B33104C0D83E9 will bring you to the shared calendar.
For each entry you make in your calendar, you can allow participants to add their name. Note that this is really on a peer-to-peer basis, so everyone with the key to your calendar can edit this list. There is no registration required, it's just quick and easy and works great for small groups. Try it in the sample calendar for the the monthly event 'Table tennis, Who's in?' Note that your entry is not stored.