There are a lot of things I can do with any object in Ruby - there's a whole package deal of methods available to me by just defining and creating an object:

irb(main):003:0> class Thing
irb(main):004:1> end
=> nil
irb(main):005:0> widget = Thing.new
=> #<Thing:0x98c1e74>
irb(main):006:0> widget.methods
=> [:nil?, :===, :=~, :!~, :eql?, :hash, :<=>, :class, :singleton_class, :clone, :dup, :initialize_dup,
:initialize_clone, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :freeze, :frozen?, :to_s, :inspect,
:methods, :singleton_methods, :protected_methods, :private_methods, :public_methods,
:instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?,
:instance_of?, :kind_of?, :is_a?, :tap, :send, :public_send, :respond_to?, :respond_to_missing?, :extend,
:display, :method, :public_method, :define_singleton_method, :object_id, :to_enum, :enum_for, :==,
:equal?, :!, :!=, :instance_eval, :instance_exec, :__send__, :__id__]
irb(main):007:0>

Question from last weeks course - But what do all of these DO?

Answer - I've added a list which describes most of them [here].
(written 2012-06-23, updated 2012-06-30)

 R108 - Ruby - More Classes and Objects
  [184] MTBF of coffee machines - (2005-01-20)
  [656] Think about your design even if you don't use full UML - (2006-03-24)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [2292] Object Orientation in Ruby - intermediate examples - (2009-07-16)
  [2601] Ruby - is_a? v instance_of? - what is the difference? - (2010-01-27)
  [2603] Ruby objects - a primer - (2010-01-29)
  [2604] Tips for writing a test program (Ruby / Python / Java) - (2010-01-29)
  [2616] Defining a static method - Java, Python and Ruby - (2010-02-01)
  [2620] Direct access to object variable (attributes) in Ruby - (2010-02-02)
  [2623] Object Oriented Ruby - new examples - (2010-02-03)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2980] Ruby - examples of regular expressions, inheritance and polymorphism - (2010-10-02)
  [3142] Private and Public - and things between - (2011-01-22)
  [3154] Changing a class later on - Ruby - (2011-02-02)
  [3158] Ruby training - some fresh examples for string handling applications - (2011-02-05)
  [3260] Ruby - a training example that puts many language elements together to demonstrate the whole - (2011-04-23)
  [3760] Why you should use objects even for short data manipulation programs in Ruby - (2012-06-10)
  [3781] Private, Protected, Public in Ruby. What about interfaces and abstract classes in Ruby? - (2012-06-23)
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [4504] Where does Ruby load modules from, and how to load from current directory - (2015-06-03)
  [4550] Build up classes into applications sharing data types in Ruby - (2015-10-23)
  [4551] Testing your new class - first steps with cucumber - (2015-10-23)

Back to Private, Protected, Public in Ruby. What about interfaces and abstract classes in Ruby?

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Forward to Load path, load and require in Ruby, and a change from 1.8 to 1.9

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Load path, load and require in Ruby, and a change from 1.8 to 1.9
Standard methods available on all objects in Ruby
Ruby of Rails - cleanly displaying model data in the view
Adding validation to form entries and sticky fields - Ruby on Rails
Providing a form to allow the user to add data to the model - Ruby on Rails
Multiple views in a single appication - sharing common parts of the template - Ruby on Rails