Pry is a powerful alternative to the standard IRB shell for Ruby. It
is written from scratch to provide a number of advanced features.

Pry also aims to be more than an IRB replacement; it is an attempt to
bring REPL driven programming to the Ruby language. It is currently
not as powerful as tools like SLIME for lisp, but that is the general
direction Pry is heading.

Pry is also fairly flexible and allows significant user customization
is trivial to set it to read from any object that has a readline
method and write to any object that has a puts method - many other
aspects of Pry are also configurable making it a good choice for
implementing custom shells.