How to organize modules

I have rails application. Now I want add there some modules. I try to
do it using plugins and have a problem. Maybe I doing something wrong.

I build module as a class. Each module has own class definition with
necessary functionality. Now I want to access them (get list of
modules for example). How should I access them?

I tried to declare a registry class in /lib and build a list of
modules them (list is filled in init.rb of each module). Then I create
a page where list of modules would be shown.

And now I have a problem.
In first access page displays everything ok. But next access displays
an empty page!

My “module registry” looks like

private_class_method :new

def self.instance
@mod = new unless @mod

def register_module (mod)
@modules = [] if !@modules
@modules << mod

def modules
@modules = [] if !@modules

What am I doing wrong? Do you have links to articles about
organization architecture like this?