as seen at freshmeat: "Gutenbook [1] is a personal multi-stage project to design, prototype, and develop a GTK+-based desktop application for reading Project Gutenberg Etexts. Currently, development consists of advanced prototyping in Perl/GTK+." According to the author, Lee, this is the original codebase from which the other Gutenbook project [2] started, but this one is purely focused on perl/gtk+ instead of multiple (incompatible) codebases.
Links:
[1] http://www.red-bean.com/~lefty/gutenbook.html
[2] http://www.llornkcor.com/software.htm