can client

A Twitter client with message store capability

Instantbird is a multi-protocol Instant Messaging client.

An IRC client for Mac OS X

Syrinx is a fully customizable twitter client designed for Leopard (OS X 10.5+).

Portable Thunderbird OS X is the popular Mozilla Thunderbird email client.

GUI Subversion client.

Xfire client implemented as a plugin for Adium.

Affordable, multi-platform client/server version control for distributed teams

Screaming fast email client.

UFxp is a GUI client for FXP.One using the Ultimate widget toolkit.