With Umbraco, it is straightforward to have a number of different websites running from the same Umbraco instance. This is useful for a business that needs different websites for products or sub-brands, whereby each site might share functionality and page layouts but where the branding and content are unique to each site.
Umbraco has multi-site capability out-of-the-box. A theme is created that is then rolled out to each website instance. This allows sites to share resources and be managed in one central location whilst retaining different domains and structures.