Every Kerika user has a unique URL that can be used to synch with his or her calendar: don't share this URL with anyone!
Open your Apple iCal calendar program and choose File > New Calendar Subscription from the menu.
Paste your unique Kerika Calendar URL when Apple prompts you for it.
And that's it.
Open Outlook and choose Open Calendar > From Internet from the menu.
Paste your unique Kerika Calendar URL when Outlook prompts you for it.
And that's it.
Open your Google Calendar.
In the left column, look for Other > Calendars and then select the Add by URL menu.
Paste your unique Kerika Calendar URL when Apple prompts you for it.
And that's it.
You can control how fast Apple, Microsoft or Google may pick up these changes from Kerika: here, for example, is you can make sure your Apple Calendar picks up changes from Kerika fairly quickly: