BBEdit, terminal. Also, not an app, but not having to screw around to make things work. This alone gives me a huge productivity boost, over Linux or Windows.

I believe that "not having to screw around to make things work" doesn't apply to windows, or at least, not anymore. Do you recall specific situations where something worked out-of-the-box on Mac but required "screwing around" on a windows machine?

Terminal. Git. Wifi. App store & re-downloading purchases. Imovie with direct YouTube upload. These all often require screwing around or installing addons in windows. All worm flawlessly out of the box (OK I movie takes 3 or 4 clicks to buy/install) on my mac. These are just the firs few things that came to mind.

Getting new devices to work (though thats probably just in the olden days as well). Also; Cygwin.

iTerm2 running tmux. That's where I run vim and irssi.

As for GUI stuff.

* Alfred - Alfred will make you 100 times more productive moving around your system.

* Spotlight - Even if you don't use Alfred, spotlight will make you more productive

* AppZapper - Uninstalls apps and removes all the little things that get left behind when dragging apps to the trash.

* Automator - A lot of people don't ever learn automator, but I think it's the best thing ever. It comes with OS X and it's awesome. I write little tasks all the time for example, I have an automator task that zips my project directory with a timestamp in the name and moves it to dropbox every day at 4:55pm for backup.

* Billings - If you do contract work Billings is amazing

* Github.app - Amazing tool

* Growl - Amazing nofitications

* LittleSnapper - Fantastic tool for keeping track of screenshots of designs and such

* Mou - Great little markdown editor

* Propane - Fantastic campfire client

* Skala Preview - Allows you to connect to photoshop and see your iOS psd's realtime on your iOS device

* Textmate - Amazing text editor

* Transmit - Best ftp client hands down

* Wakeup Time - Turns your Macbook into an alarm clock

It's only loosely an app, but having a real unix terminal (without having to run a VM) is the biggest reason I'm hooked.

Almost every Linux distro gives you a terminal. :-/

Of course! I probably should have clarified and said something like "being able to run a real terminal alongside programs like Photoshop without having to us a VM has me hooked." I love linux, but there's a lot of software I use every day that only exists for mac/windows.

I use Linux (and Solaris, and BSD ...) on a regular basis.

But whenever I use linux on the desktop, the provided terminal feels rinky-dink compared to iTerm2.

And an arguably much better terminal at that. That being said this is still a huge advantage over Windows.

Omnifocus (Omni products in general), Keynote, Alfred, Papers2, Scrivener (although there is a Windows version now), All the text editor options (Notational Velocity, Nottingham, etc)

DevonThink: I put everything in it. Great for my MSc research into concurrency.

Notational Velocity. I know about ResophNotes, etc, but they don't cut it.

iTerm2.

It's humble. But every time I use linux I find myself missing the little features that iTerm2 provides.

Alfred

Inspector and Omnifocus

MarsEdit & Coda

Pathfinder

XCode

Same here. I only have a Mac so I can develop for iOS with it.

There is no other reason to have it, in this house - everything else I do with my Mac, I can do equally well if not better with my Linux workstation.

Its just that its almost impossible to work on iOS without XCode, and so far the XCode VM I set up for the purpose isn't as performant as my MBP.

I'd love to ditch the MBP, though, and just have a plain ol' Linux workstation. I don't see anything terribly unique about OSX in comparison.

Finder

OSX itself keeps me hooked to my Mac. I can find anything I need for this platform. The whole is greater than the sum of its parts.