This is an example of a library. You may see a list of other libraries used on Rosetta Code at Category:Solutions by Library.
Wren-seq is a module which supplements the methods in the Wren programming language's Sequence and List classes with static methods in the Seq and Lst classes respectively.
It also adds new list-based FrozenList and Stack classes which do what you would expect from their names.
It is the sixth in a series of modules (listed on the language's [main page]) designed to assist with writing Rosetta Code tasks so the same code does not have to be written or copy/pasted time and time again thereby bloating a task's script code unnecessarily.
To use it you need to copy the source code (in the [talk page]) to a text file called seq.wren and place this in the same directory as the importing script so the command line interpreter can find it.
As there is a dependency on the Wren-trait module, you also need to copy that (if it is not already present) to the same directory as described [here]. Unless you are using classes in that module directly, there is no need to import them into your script and the Cloneable and CloneableSeq classes can even be imported via Wren-seq itself.