Ranked in these QuestionsQuestion Ranking
Pro GNU's official extension language
Chances are a system running enough GNU software will already have it installed.
Pro Easy to customize and extend applications
Guile makes it easy for users of your application to write extensions without needing to understand the plumbing of your program.
Pro Excellent documentation
The documentation provides conceptual overviews, tutorials, and a detailed reference for all commands, functions, and operators.
Con Weak copyleft