https://github.com/cedlemo/ruby-gtk3-tutorial
http://iridakos.com/tutorials/2018/01/25/creating-a-gtk-todo-application-with-ruby
http://bundler.io/v1.12/guides/creating_gem.html
https://relishapp.com/rspec/rspec-expectations/v/3-7/docs/built-in-matchers

CALCULATIONS: RGEO
http://daniel-azuma.com/articles/georails/part-3i -->Rgeo

INTERFACE: GOSU
https://github.com/gosu/gosu-examples
https://github.com/gosu/gosu/wiki/Getting-Started-on-Linux
https://github.com/gosu/gosu/wiki/Ruby-Tutorial