A while back, we wrote about how you can share your Google Calendar to the rest of the world. It basically involves creating a public-access calendar (or converting your calendar to public access, entirely) and sharing the RSS link for people to subscribe to. However, you may not be aware that you can actually use Google Calendar to collaborate with a select group of people.

More specifically, you can collaborate on a single calendar with other people with Google accounts. This can be very useful to professionals who work over the Internet, and don’t have physical offices nor other enterprise-grade collaborative software. Or, if you run an organization, but prefer a platform-agnostic (and not to mention inexpensive, or actually free) solution (like Lotus Notes, Outlook, iCal, or the like), a web-based solution would be a great option.

Here’s how you can use Google Calendar to collaborate.

Create a new calendar or edit an existing calendar. If you’re editing an existing calendar, look for the sharing options link.

Add users. Under sharing options, you can type email addresses of people you want to invite. The system will automatically detect if an email address is already in your Gmail contacts, and will give suggestions based on existing contacts in your list. You can choose to have your calendar read-only or editable, and this is on a per-user basis. So for instance, you can let certain users the ability to enter new calendar entries and edit existing ones. You can limit others to only viewing existing entries.

If you select “add entries and manage sharing,” this means that the user you’re adding will in effect be able to add, remove, and edit the access levels of other members of the group.

Invite users. The system will only allow users who already have Google Calendar accounts. If the system detects that the email doesn’t have a Google Calendar account yet, it will ask you if you wish to invite that person.

Accepting invitations. People you invite will get an invitation email with a link to creating a Google Calendar profile. Once they have created a calendar, they will be prompted to accept the calendar you have shared under their account.

Once the invitation is accepted, your contact can now see your calendar and can add/edit entries, as needed.