Discussion: What are your favorite mac only programs?

Obviously this week question is only for Mac users. I will soon be converting (yes, I know) to a Mac from a PC. I have owned a Mac Book Pro for a while, but did the majority of my work on my PC. As such, I never really got into aftermarket products and software for Macs.

I’m curious to see what cool programs there are out there that are for Macs only. I have seen a few scattered across the internet, but there are no doubt some really cool ones I don’t know about.

So Mac users, what are your favorite Mac only programs?