Useful Mac OS X Apps

System Related

AppleJack – User friendly troubleshooting assistant for Mac OS X
CandyBar ($$) – App for customising and organizing icons
coconutBattery – Battery monitor
Growl – Multi app notification system for Mac OS X
iStat menus – Monitors your CPU, memory, disk, network, fans etc. in a fancy GUI on your menu bar
Mac Pilot ($$) – All-in-one system app
MainMenu – Menu bar based utility app
MenuMeters – CPU, memory, disk usage meter
Monolingual – Removes unnecessary languages from your Mac OS X installation
Onyx – All-in-one system app
Quicksilver – A simple yet complex launch app that does much more
smcFanControl – Controls fan speed
Teleport – Remotely control multiple Macs
TinkerTool – All-in-one system app
Trimmit – Removes unnecessary languages from your Mac OS X installation
Unarchiver – Replacement for “BOMArchiveHelper.app”, the built-in archive unpacker program in Mac OS X
UnRarX – Mac OS X RAR extraction utility
Witch – Replacement list view for Command tab (⌘-Tab)
Xslimmer ($$) – Removes unwanted binaries, languages and code from your apps to free up disk space

Productivity

Genius – Memory based learning app
iProcrastinate ($$) – Homework and task management
Notebook 2.1($$) – Organiser
OmniFocus ($$) – Professional personal task management
SchoolHouse – Homework manager
Scrivener ($$) – Word processor and project management tool for writers
Skitch – Fast and fun screen capture and image sharing

Audio

Audacity – Open source software for recording and editing sounds
Audio Hijack Pro – Record ANY audio and output it in many different formats
Soundflower – Inter-application audio routing utility for Mac OS X
Switch – Audio conversion software

Video

Camtwist – Add special effects to your video chats
iShowU ($$) – Screen recorder
ScreenFlow – Screen recorder & video camera (vid + audio) capture
Tooble – YouTube convertor for iPods
VLC – Media player that plays almost everything

Instant Messenging

Adium – Instant Messenger (AIM, MSN, Jabber, Yahoo, etc)
Mercury Messenger – Java based messenger (feature filled but still a bit buggy)

Browsers & FTP

Camino – Native “Firefox” for Mac OS X
Transmit ($$) – FTP client

DVD Software

Burn – Burning app
Handbrake – DVD convertor

BitTorrent

Azureus – Java based BitTorrent Client
Clutch – WebUI for remotely controlling Transmission
Transmission – Lightweight BitTorrent client

Security

ClamXav – Anti-virus
Little Snitch – Outgoing connection monitor/blocker
TrueCrypt – Encryption app

Widgets

GuitarChords – Guitar chord reference
iStat pro, nano – Monitors your CPU, memory, disk, network, fans etc. in a fancy GUI on your Dashboard
This Day In History – Self explanatory

Finder Add-ons

Finder Refresh button – Refreshes Finder windows

Screensavers

Fenêtres Volantes
Fliqlo
PolarClock

($$) free trial but purchase is required thereafter

Credits:
http://opensourcemac.org
http://www.coolosxapps.net
http://www.google.com (Google is your BEST friend)

A big thank-you to Rippet for compiling the list, and n0d3 for cleaning it up.