Integration of [psysh][1] into Drush so that you can have a Drupal REPL. [1]: http://psysh.org/
drush pm-download drush_psysh
drush cc drush
drush drush-psysh-install-deps
The two following commands are aliases:
drush repl
or
drush psysh
And here's an example showing the repl in action calling a Drupal function: