Best Top Free or Opensource Mac OSX Apps Programs Software

Media Player 

VLC - VLC is free and open source cross-platform multimedia player and framework that plays most multimedia files as well as DVD, Audio CD, VCD, and various streaming protocols. 

Guitar TAB 

TuxGuitar  - Open source implementation of Guitar Pro, so far it's opened the Guitar Pro files that I've tried and able to export to midi. All free all good. 

Office Applications

OpenOffice  - The classic and legend that is OpenOffice now taken over by Oracle, still keeps it's charm for me.

Books 
Kindle - If you have a kindle this is useful to read those beloved books you've bought. But download from the Amazon website to get the more stable version. 

Virtualization

VirtualBox - Is a free virtual machine for you to install Windows or linux and run it virtual right off you desktop what more could you want. With seamless mode with Windows it's a bit weird having the task bar at the bottom of the screen. 

Torrent Client 

uTorrent - My choice for a torrent has been of late uTorrent and on OSX it looks even better. 

Browser

Chrome - With the Chrome Web Store it just gives you that more apps to have on your machine. I'll post my favourite chrome apps that will give you flexible on a whatever OS you are using.

Firefox - Needs no introduction, infamous browser Firefox.

Audio
Audacity - Opensource classic audacity audio editing tool
Ardour - Most extensive DAW environment for audio recording, but still no midi support!! argghh!

Graphics
Gimp - Again another open source hall of famer GIMP, for those who don't already know Open Source of PhotoShop
InkScape - Vector drawings

As far these are my favourites, I'll keep adding to the post as I find more.