Solution using query string

posts_example.rb

# config/routes.rb
resources :posts, :only => [:index]

# post.rb

scope :recommended,  where(:recommended => true) # having a guess on your db structure
scope :recent,  order('created_at DESC').limit(10)
scope :popular, where(:like_count => true) # again having a guess

# app/controllers/posts_controller.rb

before_filter :setup_filter, :only => :index

# The long way
# You could probably move this logic into a method on the Post model ( maybe Post.filter )
def index
  if @filter == 'recent'
    @posts = Post.recent
  elsif @filter == 'popular'
    @posts = Post.popular
  else
    @posts = Post.recommended # lets make this the default
  end
end

# Another more magic way
# This technique relies on the scopes being the same name as the filter
def index
  @posts = Post.send(@filter)
end

private

  def setup_filter
    @filter = params[:filter] || 'recommended'
  end


# so people would hit it at 
# /posts
# /posts?filter=recent
# /posts?filter=popular
#
# In your index.html.erb file you will have access to the @filter and @posts variables which you can use to render accordingly.