Provides classes that define older non-generic collections of objects, such as lists, queues, hash tables and dictionaries. Developers should prefer the generic collections in the System.Collections package. Commonly Used Types: System.Collections.ArrayList System.Collections.Hashtable System.Collections.CollectionBase System.Collections.ReadOnlyCollectionBase System.Collections.Stack System.Collections.SortedList System.Collections.DictionaryBase System.Collections.Queue System.Collections.Comparer System.Collections.CaseInsensitiveComparer When using NuGet 3.x this package requires at least version 3.4.