External libraries are collections of interfaces and classes that are of general use and thus can be reused in various projects. You won’t find many Kotlin libraries yet, but because it is easy for Kotlin to interface with Java classes and interfaces, in your projects you can use one or some of the plethora of Java libraries published by other developers and development teams.
Example fields for external libraries are encoding and decoding, compression, CSV file handling, e-mailers, higher level math and statistics, databases, extended logging facilities, XML and JSON file handling, ...
