Google Calendar

Scheduled to be in beta for the next four years.

Also, it doesn’t (yet?) support Safari, and informs you of this with a JavaScript alert that reads:

Sorry, Google Calendar does not support your browser yet, so things may break in unexpected ways.
Press OK to see a list of browsers that we support. Or cancel to try to use it anyways.

$121 billion market cap and they have someone writing error messages who thinks “anyways” is acceptable English.

★ Thursday, 13 April 2006