capistrano-send/lib/capistrano/tasks/libnotify.cap

namespace :send do
  namespace :libnotify do
    desc "Display a notification using libnotify"
    task :notify do
      if Capistrano::Send::Libnotify.supported?
        Libnotify.show(
          summary: "Deploy successful on #{fetch(:stage)}!",
          body: revision_log_message,
          timeout: 10,
        )
      end
    end
  end
end

after 'deploy:finished', 'send:libnotify:notify'