The Big Picture
What is Zulu and how does it work?
Here is the big picture: how Zulu works, and why it's cool...
Zulu turns FileMaker Server into an iCal Server (technically a CalDAV server). With this in place, iCal see's your FileMaker tables as calendars on an iCal Server: it can read them and write to them. Which tables it sees-- which tables get published as calendars-- are up to you and you'll create one record for each calendar in a new table you import into your file. This record contains the name of the calendar, it's color, which table in FileMaker it corresponds to, and what filters apply, if any. You'll also have one new layout per table that tells Zulu which fields in your table hold the record's primary key, its date field, etc.
So you can publish one table as many calendars (one calendar per user, for example, or one calendar per department). Or you can publish many different tables each as their own calendars.
Under the hood, Zulu is a server side plugin in the web publishing space. iCal sends requests to FileMaker Server via Zulu. Zulu translates these into requests the WPE can understand and, when it gets the data back, translates the results into iCal's grammar. Because of this, Zulu respects FileMaker's access privileges: when you create an account for your calendar in iCal (when you "subsribe" to the CalDAV Server) you enter a FileMaker username and password just like when you log into FileMaker and this can restrict which records you can see, edit, etc. It even goes so far as if a user is modifying a record in FileMaker and another use tries to change the record in iCal, the iCal user gets a message that someone is modifying the record. Just like in FileMaker.
Since FileMaker Server is now a CalDAV server, any app that understands CalDAV can interact with FMS. The calendars on the iPhone and iPad are great at this. Sunbird for Windows is pretty good.
Zulu lets you have ONE set of calendars (in FileMaker) that you can access from your other calendaring aps (iCal, iPhone, etc.).
Zulu can also be used to sync your FileMaker events with Google Calendar; this works much the same way in terms of multiple calendars and FileMaker access privileges, except that instead of Google making a live connection to your FileMaker Server, Zulu reaches out to Google and syncs the calendar with FileMaker. And Zulu can do this manually (there is a "sync" button on the Zulu admin page), or every X minutes / seconds.
The great thing about this is that it allows you to take advantage of all the sharing options Google Calendar offers, including the ability to embed a calendar on your web site. Google Calendar is also the best way to manipulate your FileMaker events on Android phones.
Another advantage here is that since Zulu reaches out to Google to make the sync, there are no inbound requests to your FileMaker Server. So while you may be syncing one FileMaker account to one Google account, you could have thousands of people sharing that calendar on the Google side: so you don't have 1000 inbound requests to FileMaker Server, you have 1 outbound sync every x minutes.