Drupal 6 is the easiest CMS, Content Management System to use when you want anything other than a dumb HTML page. If you start with anything less, Wordpress, you will want to change within a year because there is something too difficult for an ordinary CMS. If you start with an expensive proprietary CMS, you will kick yourself for spending all that money on software instead of your Web site.

Drupal is easy to expand with add on modules and the Domain module lets you serve many domains from one site with one database and shared data. There are not many occasions when you want to share all your data across multiple domains and the Domain module helps you limit the sharing to just the database tables required in all sites. This site demonstrates the Domain module in action.

There are alternatives to the Domain module for other combinations of domains and databases. I encourage you to look at the alternatives before plunging into the domain module.

Why have different sites and one database? Suppose you sell cars and motorcycles. One site sells Toyota cars; other site sells Moto Guzzi motorcycles, and another sells Ducati. You have customers who own a Toyota for the commute to work and rainy days plus a Moto Guzzi for cruising the highways on dry weekends plus a Ducati Desmosedici RR for the occasional really really fast trip to the shops. Why should your customers have to register three times to use the three sites when the Drupal Domain module can share their login accounts?

The spare parts people do not have to worry because the Domain module lets you specify separate parts tables for each site. The sales people in each dealership can manage their own separate price tables. you decide what you want shared and what you want separate.

The only limitation is that all the sites share all the shared data tables and that separating a table for one site will separate the table for all sites. You might have a shared service department for the motorcycles and want to share their booking diary but not share the diary with the separate car maintenance department. That type of partially shared combination is a bit beyond the Domain module.