So many awesome GUI tools for developers on Mac, I can't find on Linux. E.g. OmniGraffle is fabulous for doing diagrams. I have not found anything as well designed and functional on Linux.
You got so many nice git clients: Tower, Gitup, GitX etc. There are awesome diff tools like Kaleidoscope.
There are a lot of good tools for keeping all sorts of notes, programming snippets etc. My life is pretty much centered on Ulysses, which has a very good way of organizing and searching for notes.
Linux does of course have vim, emacs, etc but I'd say if you want a more modern feeling editor you got a lot more choices on Mac: TextMate, Sublime, SubEtaEdit, Smultron, Coda, Chocolate etc.
Then there are all sorts of specialized tools, e.g. I use a Dash a lot of looking up developer documentation. Paw is pretty neat for working with REST APIs. Base is great for looking at and manipulating SQLite databases.
Especially for any kind of graphical work, say you got to modify some application or toolbar icons, then you have a lot of great choices on Mac. Not only do you have the big powerful tools like e.g. Photoshop and Affinity Designer, but you to also small neat little tools like Pixen.
It really depends on how long you worked on the platform. I didn't use nearly as many of these tools some years back. But the longer you stay on a platform there more tools you start using as particular needs arise.
I've worked with plenty of colleagues who have used Macs for years, but who aren't really mentally into the whole Mac eco system, and so they often use various cross platform tools, websites etc before they actually explore the rich collection of desktop apps available on the Mac.