For me, that would be Secure CRT. I have yet to find a terminal emulator that matches its feature set. If you regularly manage hundreds of machines using various connection protocols (serial and ssh mostly in my case) It’s worth the $$$, and so far there hasn’t been any subscription nonsense. I liked using it at work so much I forked over the dough to have it at home.
None of the free alternatives do everything I need.
I’ll also mention a few iOS apps. One is Sun Surveyor. It’s an AR app that shows you the position of the sun, moon, and galactic center at any given time. The other would have to be Radarscope. It’s a weather radar app, but it’s a really good weather radar app.
EDIT:
This one’s debatable, but I use it all the time. Plasticity is 3D modelling software that attempts to bridge the gap between practical CAD programs and software meant for 3D artists like Blender. It’s not cheap considering Blender is free, but it’s buy once use forever, and at (I think) $150 it’s within reach of an individual hobbyist who knows what they want and is willing to pay for it.
If you’re talking functionality, I’ll introduce you to some:
Amost all paid audio production software is leagues better than the free alternatives. And beyond that, many VSTs don’t work under Linux.
The sad truth is that most Adobe products still beat their free alternatives in features. Those alternatives are definitely good enough for 95% of people but they aren’t better
Autodesk software. AutoCAD has some competition (for basic things) but there’s nothing for Revit. Actually a TON of construction/infrastructure software doesn’t have a better alternatives, not just Autodesk
Those were my 3 sticking points (I switched anyway)
AutoCAD was top of my list.
I fucking hate AutoCAD (I use it professionally) but there’s nothing better and I really doubt a free alternative can top it. AutoLISP alone makes it unbeatable