Server Management Objects (SMO) enables you programmatic access to all objects in the SQL Server service hierarchy. SMO enables you to perform tasks such as backup and restore of databases, integrity checks, and creation and scheduling of agent jobs.
Replication Management Objects (RMO) enables you to programmatically control your replication topology. Even though two assemblies need to be referenced: Microsoft.SqlServer .Rmo and Microsoft.SqlServer.Replication, only one namespace, Microsoft.SqlServer.Replication needs to be referenced in the code.
Analysis Management Objects (AMO) enables you to programmatically control your SQL Server Analysis Server (SSAS) objects, which include cubes, dimensions, and mining structures.
Multiple Active Result Sets (MARS) is a new feature that enables you to perform multiple database operations using the same connection. This helps to avoid locking that you might have encountered in the past.