Has a Built-In Common Type System ! Is Extensible ! NET Framework class library exposes features of the runtime and provides other high-level services that every developer needs. NET Framework class library, classes are grouped into namespaces. The first part of the full name, which is located before the rightmost dot, is the namespace name. The last part of the name, which is located after the dot, is the type name. Collections namespace. Collections namespace can be used to manipulate collections of objects.