Pachi
Pachi is an open source go playing program (engine) or go-bot. It is being actively developed.
It reached 4d on kgs server (account Pachi2 cluster version)
See latest go software updates for the latest update news.
Homepage is at http://pachi.or.cz/.
Online webapp http://www.peepo.com with maps and comments as you play
please use latest Firefox or another standards-based browser, in case of difficulty.
The source code, written in C, is available at http://repo.or.cz/w/pachi.git.
Windows binaries (include Makefile for MinGW) are downloadable at http://pachi.or.cz/.
Mac binary is available in the Sente Goban extension package at http://www.sente.ch/?p=1221&lang=en.
The successive versions of the program are named after famous Japanese players:
Pachi 2.00 September 2008 Sana? Pachi 3.00 October 2009 Sanetsu Pachi 4.00 October 2009 Doetsu Pachi 5.00 Februari 2010 Dosaku .... Pachi 8.00 May 2011 Shuhaku Pachi 9.00 October 2011 Hakugen Pachi 10.00 August 2012 Satsugen