Facebook application on Orkut
Digg on Orkut
Reddit application on Orkut
If you want any of these open social applications on orkut, you need an account on http://sandbox.orkut.com. You can apply for the sandox here http://code.google.com/support/opensocialsignup/. Once you have access to the sandbox goto http://sandbox.orkut.com/MyApps.aspx and use the following urls to access the applications.
Facebook Application - http://vivekjishtu.com/opensocial/facebook.xml
Digg Application - http://vivekjishtu.com/opensocial/digg.xml
Reddit Application - http://vivekjishtu.com/opensocial/reddit.xml
They are nothing more than simple iframes but it defiantly seems cool the first time you see it.