I think Erik Nordin created the pagetypebuilder tool: http://pagetypebuilder.codeplex.com/
Alf Nilsson has done some tool for EPi7: http://talk.alfnilsson.se/2013/03/08/creating-page-type-classes-from-page-types-in-episerver-cms-7/
You're probably thinking of this plugin by Erik Nordin: http://antecknat.se/blog/2009/11/02/creating-classes-for-pagetypebuilder-in-an-existing-project/
Alf Nilsson ported it to work with EPi7: http://talk.alfnilsson.se/2013/03/08/creating-page-type-classes-from-page-types-in-episerver-cms-7/
EDIT: Per beat me to it while I was typing, although his link is to the Page Type Builder project by Joel Abrahamsson, not Erik's plugin :-)
Haha friday night WIN ;)
For EPiServer 7 there is actually a hidden built in tool in Admin mode: /CMS/Admin/PageTypeCodeGenerator.aspx. It uses some old attribute names, but it can be easily fixed since all code is inside this aspx file.
Hey, does anyone remember that tool that exported page types from database to PageTypeBuilder classes? I can't Google it any more and I didn't save it anywhere :(
Also, do you know of the same tool for EPi7?