I work on large system performance simulation and modeling at Oracle. I intend to hack on my long list of half-started Cocoa projects someday, but who knows when that'll be.
Active Cocoa Projects That I'm Not Involved in Anymore
Skim, a PDF reader that improves on Preview: http://skim-app.sourceforge.net/ (I helped a bit with design but only contribute occasionally)
It was a web site that allows you to search through the source code of several open source projects.