If your application has certain events(For example meeting etc), then you may need to integrate calendar application.
Icalendar is a standard for calendar data exchange.
Icalendar allows us to generate .ics files so that users can add events to their calendars.

First of all install the gem

gem install icalendar

And run bundle install
After this add require 'icalendar' to your config/environment.rb

Suppose we have a MeetingEvent model:

class MeetingEvent < ActiveRecord::Base

# Table name: meeings_events
#
#  id           :integer(11)     not null, primary key
#  title        :string(255)
#  start_date    :datetime
#  end_date     :datetime
#  summary      :text
#  created_at   :datetime
#  updated_at   :datetime
end

The next part is added "to_icalender" action of the MeetingController to accept .ics format:

def to_icalender
        @event = MeetingEvent.find(params[:id])
        respond_to do |format|
          format.html
          format.ics do
            cal = Icalendar::Calendar.new           
                event = Icalendar::Event.new
                event.dtstart = @event.starts_at
                event.dtend = @event.ends_at  
                event.summary = @event.title
                event.uid = event.url = "#{event_url}"
                cal.add_event(event)            
                cal.publish
                render :text =>  cal.to_ical
          end
        end
    end

Add a link to your view:

<%= link_to @event.title, :controller => 'meeting', :action => :to_icalender, :format => :ics %>