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.
Total Commander on Windows. It can be used for free with the nag dialog, but I paid for it since I was using it every day.
Automate on Android: it’s an automation tool with its own programming ‘language’ like Tasker, except visual. Tasker has some weird and cumbersome idioms, while Automate is mostly regular programming mapped onto its visual blocks. Plus it doesn’t require buying more apps for additional functionality like Tasker. Alas, it can’t do custom dialogs or onscreen buttons, so I might still need Tasker for that.
Unified Remote on Android: nice remote control for the desktop machine, with the ability to add custom controls programmed in Lua (iirc).
Magic Dosbox on Android: it allows adding custom onscreen controls tailored to each game.
Functional Ear Trainer and Perfect Ear on Android: nice training for hearing notes and rhythm, though I can’t say they did much for my lazy ass.
Sunvox on Android: a music tracker with modular synths. Seems to be the only full-blown tracker on Android. Alas, doesn’t seem to be very good with samples, the workflow is a bit cumbersome, but I need to properly try that yet. The app has been around for ages, I’ve seen it twenty years ago for Palm and Windows CE. There are also desktop versions, which are free iirc. (Also, the author can’t currently receive payments from Google Play since he’s in Russia. It’s better to write to him and arrange payment via bitcoin or such, afaik he’s happy to provide the full app that way.)
On Mac, there are many open-source utils for tweaking the interface, but paid Bartender and Hazeover are better than alternatives. One hides extra menu icons, the other dims background windows.
Alfred on Mac, a launcher: you call it up with a hotkey, and type a few letters to run an app or, crucially, a custom action. It’s unmatched by alternatives, especially on Windows and Linux. Typing a couple letters into Alfred is often quicker than cmd-tabbing to an app. And it’s way better for frequent actions than mousing around.
I’m also planning to buy Renoise, the cross-platform music tracker. It does about everything the big DAWs do, but with the keyboard-centric workflow. Pretty cheap too.
I also use Total Commander for Android. It’s the only file manager on Android that makes sense to me.
Yeah, the Android app is great, and is free. The open-source Ghost Commander is lacking in polish in comparison.
The only thing I’m missing from TC on Android is filtering the list with keyboard entry instead of jumping to the file that begins with those letters. The former is much better, as shown by Double Commander.