For Commenting Systems

aspcomments
http://www.sneaker.org/index.html

Comment system that does not require server installation.

blogKomm
http://blogkomm.com/index.php

PHP-based system to integrate comments directly into a blog

cgiComments
http://www.knurdle.com/commenting.php

Free perl-based comment system for use on Blogger-backed and other weblogs.

dotcomments
http://www.foreword.net/

Hosted commenting system for Blogger-based blogs

YACCS
http://rateyourmusic.com/yaccs/

"Commenting made simple"

For Posting APIs and Tools

AvantBlog
http://www.dentedreality.com.au/avantblog/

Windows front-end to Blogger.

Bloggenmoz
http://bloggenmoz.antville.org/topics/download

Blogger API support for Mozilla Composer

Blogger API
http://www.blogger.com/developers/api/

Details of the XML-RPC interface to Blogger

BloggerBot
http://www.fibiger.org/bloggerbot/

AIM client for Blogger.

bloggerCOM
http://www.fibiger.org/bloggerbot/

COM interface to the Blogger API

BlogniX
http://blognix.sourceforge.net/

Free-Conversant
http://www.free-conversant.com/

Online discussion group tool that provides server space. Follow the "support" link for information on their weblog features.

LUSENET

http://www.greenspun.com/bboard/index.tcl

Online weblog creation tool that requires you to have a server somewhere that can accept updates via ftp.

BOP

http://sourceforge.net/projects/bop/

BOP Stands for "Blog Oriented Publishing", an open source database-backed system written in perl. Still in early alpha and looking for contributors.

pMachine

http://www.pmachine.com/

PHP/MySQL system with many features beyond weblog maintenance, including mailing lists and dynamic content management.

WikiWeblogPM

http://www.ourpla.net/john/wikiweblogpim.html     

A "page of links on research about things relevant to software that would combine the best features of existing wiki, weblog and PIM software."

Blog Rolling Competitions

http://www.webtechniques.com/archives/2001/01/jepson/

Comparative review of Slash, Squishdot, and Thatware.

Weblog

http://www.webreference.com/perl/tutorial/17/index.html

Despite the name, this is software for maintaining RSS channels rather than conventional weblogs, though it does offer HTML output features as well.