Essential Mac OS X Apps (Freeware)

Below is a list of apps essential for any Mac OS X installation. Especially useful for recent switchers or for experienced users who may not know about one or two of these apps. I'll add to this list over time; feel free to post suggestions in the comments.

Adium

Adium is a highly customisable multi-protocol instant messenger. It supports AIM, MSN, Jabber, Facebook Chat and more.
www.adium.im

Growl

Growl provides system-wide notifications for OS X apps that support it. For example Adium uses it to notify you when a contact comes online.
www.growl.info

Quicksilver

Quicksilver is an application launcher with much more functionality including playing a song in iTunes, sending an e-mail, running a script and more; all with just a few keystrokes.
www.blacktree.com

The Unarchiver

The Unarchiver is a very clean and simple decompressing app. It supports a lot more formats than the built-in OS X decompressor.
wakaba.c3.cx/s/apps/unarchiver.html

Burn

Burn is a feature-rich disc burning app with a very simple and easy to use interface. It automatically converts your content to the right format before burning and also has advanced options for DVD-Video burning, such as built in themes for custom menus.
burn-osx.sourceforge.net

Smultron

Smultron is a replacement for TextEdit that maintains the same simplicity, however it has advanced features like syntax highlighting.
NOTE: Smultron is no longer in active development, however there is a BETA available for Snow Leopard which fixes a lot of bugs introduced by the OS.
www.sourceforge.net/projects/smultron/

Multiclutch

Multiclutch is a very useful app for Apple notebooks with trackpads that support multi-touch. It allows you to assign gestures to a keyboard shortcut in a specific app. For example you can set Safari to change tabs when you swipe left and right on the trackpad (Cmd+Shift+[ and Cmd+Shift+] shortcuts).
NOTE: In order for MultiClutch to work with Snow Leopard apps you must run the app in 32-bit mode. Do this by right clicking on the app, clicking 'Get Info' and checking 'Open in 32-bit mode'.
www.wcrawford.org/2008/02/28/everytime-i-think-about-you-i-touch-my-cell/

Perian

Perian is a QuickTime component that adds native support for many popular video formats.
www.perian.org

Flip4Mac

Flip4Mac is another QuickTime component that allows you to play Windows Media Video formats.
www.telestream.net/flip4mac-wmv