From the README:

  Twisted is an event-based framework for Internet applications.  It includes
  a web server, a telnet server, a chat server, a news server, a generic
  client and server for remote object access, and APIs for creating new
  protocols and services. Twisted supports integration of the Tk, GTK+, Qt or
  wxPython event loop with its main event loop. The Win32 event loop is also
  supported, as is basic support for running servers on top of Jython.

Twisted is based on an unconventional and somewhat Twisted design philosophy.

WWW: http://twistedmatrix.com/