Redmine

That's not a job for a hook, but yes, this should be extendable...

Any update to this?

As of version 1.0.0.stable I have managed to incorporate search to a plugin with the following changes:

1. Provide search scope in the controller. For example for EzPlugin I had to write
   

   class EzfaqController < ApplicationController
   [...]
     default_search_scope :faqs
   [...]
   

2. Provide ability to search in the model (In EzPlugin it's already in the plugin)
   

   class Faq < ActiveRecord::Base
   [...]
     acts_as_searchable :columns => ["#{table_name}.question", "#{table_name}.answer"],
                           :include => [:project]
   [...]
   

3. Register the plugin in Redmine search (libs/redmine.rb)
   

   Redmine::Search.map do |search|
   [...]
     search.register :faqs
   [...]