SPOON allows you to design ETTL transformation using a GUI. For example, extracting information from an SAP system and storing it into a text-file looks like this:
http://kettle.pentaho.org/images/products_spoon.jpg
Steps
A step is one part of a transformation. Steps can provide you with a wide range of functionality ranging from reading text-files to implementing slowly changing dimensions.
Step types
Documentation
For more information on Spoon, please check out the Spoon documentation (PDF link).