A button can be used to grab text from an external command and display it as a para. The top command on Linux is used to show the CPU and memory utilization of all the processes running on the system. If you're not using Linux, you can replace the top command with any other command (including one of your Ruby scripts) to be displayed in the window.
The only thing different about this example is the font settings for the para. This is for two reasons. Firstly, a mono-space font must be used or the table displayed by the top command won't be formatted correctly. Secondly, a smaller font must be used or it won't all fit in the window.
Shoes.app :width => 600, :height => 400 do
button "What's eat up all of my memory?" do
para `top -b -n1`, :font => 'Cou rier 12px'
@p = flow