align.el

;; my answer
(defun align-to-comma (begin end)
  "Align region to comma signs"
  (interactive "r")
  (align-regexp begin end
                ",\\(\\s-*\\)[^# \t\n]" 1 1))




;;;;
(defun align-to-comma (begin end)
  "Align region to comma  signs"
  (interactive "r")
   (align-regexp begin end
                 (rx (group (zero-or-more (syntax whitespace))) ",") 1 1 ))


;; or comma not refactor
(defun align-to-comma2 (begin end)
  "Align region to equal signs"
   (interactive "r")
   (align-regexp begin end "\\(\\s-+\\)," 1 1 ))

gistfile2.rb

# FROM:
class Demo
  property :id, Ciao
  property :demo, String
  property :foo, Bar
end


# with my align.el
class Demo
  property :id   , Ciao
  property :demo , String
  property :foo  , Bar
end


# my target is:
class Demo
  property :id,   Ciao
  property :demo, String
  property :foo,  Bar
end