DeepDive is a ruby gem that allows you to deep copy your object graphs in a controlled way. You can specify which instance variables to skip over in the duplication, which will just leave the original reference to them in the copy.
Create of Local Copy of the famous EMSL Basis Set Exhange. No more lag and a API for scripting.
Copy of the UI portion of the Ocean (very much in progress). Ember.js app.
Copy of FreeGLUT's svn repo on sourceforge, for easy contribution
A Firefox plugin to copy data from a CSV file into online forms.