How can I get gedit ready for programming in Ruby and Ruby on Rails?

simply

sudo apt-add-repository ppa:ubuntu-on-rails/ppa
sudo apt-get update
sudo apt-get install gedit-gmate

and activate the plugins you want from options menu. It will activate sintax highlighting for erb files and many snippets for RoR developing.

Some more hints can be found here: https://rbjl.janlelis.com/22-rubybuntu-4-make-gedit-better-than-any-ide. Some commands for the "external commands" plugin (e.g. "run in irb") can be found in this post: https://rbjl.janlelis.com/23-gedit-external-tools-ruby-helpers-git-integration-and-more

2020 Update: As Crimbo noted, this might be outdated now...