Vectorworks uses a system of Groups, Symbols, Classes and Layers, which is very powerful.

Groups act as 'boxes', organising the drawing into discrete sections. A duplicate group is independent from the original. Groups aren't named, they're simply a drawing tool that allows disparate objects to be linked for convenience.

Symbols are clones - similar to a SU component. Change any symbol and it updates across the file. Useful for repetitive elements (obviously), such as standard size doors, they're named and organised in a library (which can be referenced from an external file). Symbols can be automatically inserted into walls in the manner of SU, but this is complex and not that important in practice - it's the ease of updating that's particularly useful.

Classes are the equivalent of Moi names. Classes can set global properties - colours, lineweights, opacity, visibility and so on. Classes operate drawing-wide, affecting members of groups and elements. Useful for grouping materials.

Layers are the equivalent of separate drawing sheets overlaid (storeys of a building for example). They can probably be discounted here.

The system works well, and would certainly help me in my use of Moi - I find it too easy to change something by accident..