View Extender

In your views put

<% extension_point 'my_extension_point_name' %>

Or

<% extension_point 'my_extension_point_name' do %>
  <div> DEFAULT CONTENT TO BE ALTERED </div>
  <%= link_to 'My Widget', widget_path(@widget) %>
<% end %>

Plugins, etc can then add to this view via:

# specify a string to put in the output
ViewExtender.register('my_extension_point', :bottom, 'my_key', "STRING TO OUTPUT")

# make a call to the render method at the specified point
ViewExtender.register('my_extension_point', :top, 'my_key', :partial => 'partial_file')

# dynamically build a render call
ViewExtender.register('my_extension_point', :replace, 'my_key') do
  :partial => Configuration.feature_x_enabled? ? 'feature_x' : 'no_feature_x'
end

There can be any number of extensions at a single point. They will be displayed in the order they are added. They can be removed via

ViewExtender.unregister('my_extension_point', 'my_key')

The positions you can extend are :before/:top, :replace, :bottom/:after. You can use :replace with a block to either replace it, or if the block returns nil, do nothing.