An open source Mac OSX RSS reader with support for RSS/Atom feeds
Vienna is an open source Mac OSX RSS reader with support for RSS/Atom feeds, article storage and management via a SQLite database, written in Objective-C and Cocoa. Feeds can be accessed directly, or through a syncing service supporting the Open Reader API, like BazQux.com, FeedHQ.org, InoReader.com or TheOldReader.com. Development now happens on GitHub: https://github.com/ViennaRSS/vienna-rss
Smultron is a text editor written in Cocoa for Mac OS X Leopard 10.5 which is designed to be both easy to use and powerful.
A multi-protocol instant messaging app for Mac OS X
Adium is an Open Source, multi-protocol instant messaging application for Mac OS X. Adium supports AIM, ICQ, Jabber, MSN, Yahoo!, Google Talk, Bonjour, Gadu-Gadu, Novell Groupwise, SIP/SIMPLE (Text), and Lotus Sametime. Additionally, it supports all of these applications at once so, even if you have multiple IM accounts, you don't have to log into each account separately.