Py6502, an NMOS 6502 microprocessor simulator.

Based in part by C source code from Earle F. Philhower III, 
Commodore 64 Emulator v0.3, (C)1993-94.  Other portions,
including cycle time calculations, were derived from JavaScript
work by Norbert Landsteiner, 2005.  All other work is by
Mike Naberezny.  The excellent book "Programming the 6502" by 
Rodnay Zaks was also referenced extensively during the development 
of this software.

For a quick introduction to Py65, see this post:
http://mikenaberezny.com/2008/07/01/py65-6502-microprocessor-simulator/

For more information on the 6502 microprocessor, visit http://6502.org.