What keeps me on macOS #

Carbon Copy Cloner - Legendary bootable backups and imaging
Cardhop & Fantastical - Salvation from Apple's feckless Contacts & Calendar apps
Coda - The only way to web
Fileloupe - Former BeOS and Finder engineer builds a better image browser
MacDown - Make writing fast and fun again
MacPorts / Homebrew - apt for Mac
Monodraw - Visio meets ASCII art
Notational Velocity - A near religious experience after Notes.app
QuickBooks 2016 for Mac - Surprisingly pleasant bookkeeping¹
Reeder - Celebrate Google Reader's retirement
Safari - Because web browsing is slow enough as is
Shortcat - Keep your hands on the keyboard
Spectacle - Move and resize windows with ease
Sublime Text - Text editing at the speed of thought²
Together 2.6.8 - The only laggard in the bunch, but well worth the wait if you need a free-form, tree-style database that stores data in standard files and folders within the Finder
VMWware Fusion - Run all the things!³
Mid 2012 MacBook Pro - The Toyota FJ40 of MacBooks
Built-in trackpad - Simply without peer
Cook's apparent devotion to user privacy and security (as long as you're not in China)

Footnotes:

The Windows version is much clunkier. ~~Reportedly, 2016 is the final desktop version for Mac~~. (UPDATE: Just learned from an Intuit customer service rep that a 2019 version for Mac is planned.) Still available at a discount from Intuit via this curiously-obscure page.
Yes, it's available for other platforms as well, but without Sublime Text I'd be sorely tempted to jump ship.
Other platforms also enjoy plenty of virtualization options, none of which run OS X / macOS guests easily and/or legally.

/mac | May 09, 2018