HotRuby是一个在Javascript和flash上的虚拟机上跑ruby代码并编译成opcode的项目。
你可以通过在网页上嵌入<script type=”text/ruby”>…</script>并在之间写ruby脚本。HotRuby会识别并编译为远程脚本然后由javascript和flash的虚拟机来执行，显示在页面上。这里演示一个demo，包括一个物理学应用，一组碰撞球和一个速度测试。（在我机器上，使用HotRuby要比Ruby1.9快了78%）

$n = $native
$n.import "Box2D.Dynamics.*"
$n.import "Box2D.Collision.*"
$n.import "Box2D.Collision.Shapes.*"
$n.import "Box2D.Dynamics.Joints.*"
$n.import "Box2D.Dynamics.Contacts.*"
$n.import "Box2D.Common.Math.*"
$n.import "flash.events.*"
$n.import "flash.display.*"
$n.import "flash.text.*"
$n.import "General.*"
$n.import "TestBed.*"

class Box2D
  def initialize
    @curr_id = 1
    @curr_test = nil
    
    add_fps_counter
    add_sprite
    add_instructions_text
    add_about_text
    add_input_fix_sprite
    add_listener
  end

  def add_listener
    update = Proc.new{|evt|
      # clear for rendering
      @sprite.graphics.clear
      
      # toggle between tests
      if $n.Input.isKeyPressed 39 then # Right Arrow
        @curr_id = @curr_id + 1
        @curr_test = nil
      elsif $n.Input.isKeyPressed 37 then # Left Arrow
        @curr_id = @curr_id - 1
        @curr_test = nil
      # Reset
      elsif $n.Input.isKeyPressed 82 then # R
        @curr_test = nil
      end
      
      # if nil, set new test
      if nil == @curr_test then
        case @curr_id
        # Bridge
        when 0
          @curr_test = $n.TestBridge.new
        # Example
        when 1
          @curr_test = $n.TestExample.new
        # Ragdoll
        when 2
          @curr_test = $n.TestRagdoll.new
        # Compound
        when 3
          @curr_test = $n.TestCompound.new
        # Stack
        when 4
          @curr_test = $n.TestStack.new
        # Crank
        when 5
          @curr_test = $n.TestCrank.new
        # Pulley
        when 6
          @curr_test = $n.TestPulley.new
        # Gears
        when 7
          @curr_test = $n.TestGears.new
        # Wrap around
        else
          if @curr_id < 0 then
            @curr_id = 7
            @curr_test = $n.TestGears.new
          else
            @curr_id = 0
            @curr_test = $n.TestBridge.new
          end
        end
      end
      
      # update current test
      @curr_test.Update
      
      # Update input (last)
      $n.Input.update
      
      # update counter and limit framerate
      @fps_counter.update
      $n.FRateLimiter.limitFrame 30
    }

    $n._root.addEventListener $n.Event.ENTER_FRAME, update, false, 0, true
  end

  def add_fps_counter
    @fps_counter = $n.FpsCounter.new
    @fps_counter.x = 7
    @fps_counter.y = 5
    $n.Main.m_fpsCounter = @fps_counter
    $n._root.addChildAt @fps_counter, 0
  end
  
  def add_sprite
    @sprite = $n.Sprite.new
    $n.Main.m_sprite = @sprite
    $n._root.addChild @sprite

    @input = $n.Input.new @sprite
  end

  #Instructions Text
  def add_instructions_text
    instructions_text = $n.TextField.new

    instructions_text_format = $n.TextFormat.new "Arial", 16, 0xffffff, false, false, false
    instructions_text_format.align = $n.TextFormatAlign.RIGHT

    instructions_text.defaultTextFormat = instructions_text_format
    instructions_text.x = 140
    instructions_text.y = 4.5
    instructions_text.width = 495
    instructions_text.height = 61
    instructions_text.text = "Box2DFlashAS3 examples: \n'Left'/'Right' arrows to go to previous/next example. \n'R' to reset."
    $n._root.addChild instructions_text
  end

  # textfield pointer
  def add_about_text
    aboutTextFormat = $n.TextFormat.new "Arial", 16, 0x00CCFF, true, false, false
    aboutTextFormat.align = $n.TextFormatAlign.RIGHT

    about_text = $n.TextField.new
    about_text.defaultTextFormat = aboutTextFormat
    about_text.x = 434
    about_text.y = 71
    about_text.width = 200
    about_text.height = 30
    $n.Main.m_aboutText = about_text
    $n._root.addChild about_text
  end

  # Make a big invisible box to cover the stage so that input focus doesn't change when mousing over the textfields
  # (Please let me know if there's a better way to solve this problem) (:
  def add_input_fix_sprite
    inputFixSprite = $n.Sprite.new
    inputFixSprite.graphics.lineStyle 0,0,0
    inputFixSprite.graphics.beginFill 0,0
    inputFixSprite.graphics.moveTo -10000, -10000
    inputFixSprite.graphics.lineTo 10000, -10000
    inputFixSprite.graphics.lineTo 10000, 10000
    inputFixSprite.graphics.lineTo -10000, 10000
    inputFixSprite.graphics.endFill
    $n._root.addChild inputFixSprite
  end
end

Box2D.new