Ranked in these QuestionsQuestion Ranking
Pro It is Common Lisp
Lisps are easy languages to learn (once you get past the parens) and Common Lisp is a very practical dialect.
Pro Run almost identically on both the browser and server
Pro Interactive REPL
You can evaluate new Python code in the browser written by the user.
Con The syntax may be hard to learn
Being an implementation of Lisp, Parenscript's syntax may seem cryptic and hard to understand for people not used to it. While Lisp has very little syntax compared to other languages and it's generally considered pretty terse, there's still an initial overhead in learning the language.
Con Python 2.6
Skulpt implements an outdated version of the Python language.