Libsigc++ is part of the greater GNOME code base.

• gtkmm widget wrapper
• GTK+ widget set
• Gnome project

There are a number of other C++ callback systems and publications on construction of callback systems.

• Trolltech signal system (part of Qt widget set)
• (Send us a link you find worth mentioning here.)

Additionally, these sites provided valuable help in creating this library.

• Esa Pulkkinen's programming techniques page
• C++ Tip-of-the-Day

Here is a list of some of the projects that use libsigc++. (Have a project which is using libsigc++? Mail us.)

• Libpropc++: Creating and effective using properties in C++
• Yehia: Extension library with support for cross-threaded signal emission.
• GFC: Alternative C++ wrapper for the GTK+ widget set.
• Libuta
• The WorldForge Project

This is just a list of sites that point to libsigc++. It should help you find similar libraries and related resources. (somewhat sorted by relevance)

• Linux Game Development Center
• The GUI Toolkit/Framework Page
• Available C++ Libraries FAQ
• Freshmeat
• Linux Berg
• Linux Links
• Mathtools.net