Peggy helps you to create GTK applications that run out-of-the-egg. It offers functions to load resources (like .glade files, images, and locales) from a zipped or unzipped egg. It is a thin layer on top of setuptools and PyGtk. It doesn't do anything very fancy, but it can save you from reading some documentation.
PyORBit is a Python binding for the ORBit2 CORBA ORB. It was developped to suit the needs of the bonobo bindings in GNOME-Python, but is usable for other purposes as well. It aims to follow the standard Python language mapping for CORBA. It can generate stubs at runtime from typelibs, IDL files, or by introspecting remote objects using ORBit2's IModule typelib capabilities.
Libxslt is a C library for GNOME which allows developers to work with XSLT. It is based on libxml for XML parsing, tree manipulation, and XPath support. Also included is 'xsltproc', a command line XSLT processor. The library is written in plain C, making as few assumptions as possible, and sticking closely to ANSI C/POSIX for easy embedding. It should work on Linux, Unix, and Windows. Though not designed primarily with performances in mind, libxslt seems to be a relatively fast processor. It also include full support for the EXSLT set of extension functions as well as some common extensions present in other XSLT engines.