Ruby vs C# - http://blog.cypok.info/2009/02/ruby-vs-c.html

list.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace DoubleLinkedList
{
    class ListNode
    {
        public ListNode next;
        public ListNode prev;
        public int value;

        public ListNode(int value)
        {
            this.value = value;
            this.prev = null;
            this.next = null;
        }

        public ListNode(int value, ListNode prev, ListNode next)
        {
            this.value = value;
            this.prev = prev;
            this.next = next;
        }
    }

    class List
    {
        private ListNode head;
        private ListNode tail;

        public List()
        { 
            head = tail = null;
        }

        public List PushBack(int value)
        {
            if ( tail == null )
            {
                tail = head = new ListNode(value);
            }
            else
            {
                tail.next = new ListNode(value, tail, null);
                tail = tail.next;
            }
            return this;
        }

        public List PushFront(int value)
        {
            if ( head == null )
            {
                tail = head = new ListNode(value);
            }
            else
            {
                head.prev = new ListNode(value, null, head);
                head = head.prev;
            }
            return this;
        }

        public override string ToString()
        {
            if (head == null)
                return "";
            
            ListNode elem = head;
            string result = elem.value.ToString();
            while( (elem = elem.next) != null)
                result += " " + elem.value.ToString();
            return result;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            List list = new List();
            list.PushBack(3);
            list.PushFront(4);
            list.PushBack(8);
            list.PushBack(9);
            Console.Write(list);
        }
    }
}

list.rb

class ListNode
  attr_accessor :prv, :nxt, :value

  def initialize(value, options = {})
    @value, @prv, @nxt = value, options[:prv], options[:nxt]
  end
end

class List
  def initialize
    @head = @tail = nil
  end

  def push(place, value)
    unless @head
      @head = @tail = ListNode.new( value )
    else
      case place
      when :front
        @head.prv = ListNode.new value, :nxt => @head
        @head = @head.prv
      when :back
        @tail.nxt = ListNode.new value, :prv => @tail
        @tail = @tail.nxt
      end
    end
    self
  end

  def to_s
    return "" unless @head
    elem = @head
    result = "#{@head.value}"
    result += " #{elem.value}" while elem = elem.nxt
    result
  end
end

list = List.new
list.push :back, 3
list.push :front, 4
list.push( :back, 8).push( :back, 9 )
puts list