Since I recommend these gems on a daily basis in various IRC-channels I wrote up all the development gems we use to make our lives easier.
Most of the gems are Rails specific but there should be something for every Ruby developer.
Powerful IRB replacement
teaches Pry about step, next and continue commands
Press a shortcut, click on whatever on your page, be in the view/partial
Hides asset requests from your development.log
Openes every delivered email in your browser, join the safe side ;)
=> See the full list on our blog