task_manager.rb

class User < ActiveRecord::Base
  has_many :tasks
  #common attributes and behavior for managers and workers
end

class Manager < User
  #special manager's attributes and behavior
end

class Worker < User
  #special worker's attributes and behavior
end

class Task < ActiveRecord::Base
  belongs_to :manager
  belongs_to :user
end

#Migration: create_user.rb
CREATE TABLE users (
   id INT NOT NULL AUTO_INCREMENT,
   user VARCHAR(15) NOT NULL UNIQUE,
   pass VARCHAR(40) NOT NULL,
   type VARCHAR(20) NOT NULL,
   PRIMARY KEY (id)
);

Is that Ruby Language?

yes, it is
Is an inheritance in Ruby on Rails