One Essential App
On the Mac, iPad, or phone what one app makes the device worth using. Productive tool, life enhancing, serious, fun… frequently mentioned or odd duck… Please specify the device(s) you are using.
iPad and phone
My selection Paprika qualifies as frequently mentioned, fun, and life enhancing. I use the app to collect and store Internet recipes. My last stop for some Keto ideas.
For me it’s loopback 2. Being able to easily combine audio and move it to wherever it needs to go is so easy.
For my wife it’ll be the iPad, so Procreate without any pause. Her iPad Pro is basically a drawing tablet with a few extra features.
For me on my Mac it’s a bit tougher as it changes with the seasons/hobbies. Right now we’re building a house, so I’ll pick Graphic, which has let me do all the drawings with precision and ease (plus they sync to my iPad). I also like how it is scriptable, although sometimes just creating external macros with Keyboard Maestro is simpler.
Nice to see some love for Graphic - I’ve been using it off and on since it was iDraw, for everything from wedding invitations to Alfred remote icons.
Can I add one for iPad? I’m going to anyways lol: OnSong which holds all of my chord charts and Prime, which is a free app that runs my backing tracks.
Evernote would have to be my standby/everything app. For more than a few years of college, it captured practically every shred of documentation and notes for all my classes, and was my primary implementation of GTD for much of work outside of class.
Omnifocus, without which I could not function nearly as efficiently or easily.
With DEVONTHink a strong runnerup.
Those 2 are the primary apps that keep me in the Mac ecosystem.
Very hard to pick one, I have four Ulysses, Launchbar, Keyboard Maestro and DEVONthink that really function together for me. I think of them almost as one thing if I can put it that way. If I was forced to choose it would have to be DEVONthink though it would be a close call and it would just be a case of finding replacements of the others, is that an option though for your question?
In that case Alfred, NValt and Text Expander. There is no real replacement for Keyboard Maestro that I know of?
I agree with you about Paprika. I love that app. Nothing cooler than cooking with your iPad in the kitchen with you.
I found that annotating PDFs on an iPad, especially with an Apple Pencil is fantastic. So using a tool like PDF Expert or GoodNotes has really been awesome for me. I loathe doing markups on paper now.
On Mac, i have to say Scrivenr is really amazing and is the best writing tool I’ve ever used. The app thinks like I do, it seems! I agree that utilities, like Launchbar or others really do make using macOS smooth, efficient, and fun.
OmniFocus on iPad and Mac is also an essential for me. It sees everything together and has empowered my ability to move seamlessly from device to device and to be able to work (or not work) from wherever I am on, above, or under the planet.
I know this is technically more than a single essential app. I didn’t mean to break the rule, but these apps all kind of work together as a cohesive unit.
My app that is totally Mac and I essential is Preview.
I love this app. I work with pdfs all day long, and it is fast, capable, and embedded in OSX.
When I have someone coming from the darkside, they just are not used to working with pdfs. I have to imagine that Windows has the capability now (outside of the beastly and expensive Acrobat).
I only have to go outside Preview if I need to do heavy editing.
You touched on a concern I had in my original post. There are clusters of apps that count as one. I ended up choosing Paprika because I use it daily and adds to thefun element of iPad ownership.
On the other hand, I use Ulysses daily and know it’s ins and outs, strengths and weaknesses. But then I’d start clustering the WP Editor, Terminology…
My essential app is Omnifocus (Mac, iPhone and iPad). I use it so much that my brain sometimes thinks as Omnifocus!
Good points, I weight the fun side too. It is a way of culling some less important apps too I guess? Good question really.
Given today I am chopping and scanning a few paperbacks I will pick ScanSnap Home software application. I have the IX500 and once I updated the software I continued on my merry paperless life. The transition was wacky but I use it all the time and edit in preview. I don’t save anything within the app.
Same. Evernote without a doubt. Almost 13,000 notes, I live and die by this thing. And if I died you could reconstruct me from my second brain! 
In terms of sheer use, Duet is the app that keeps my iPad productively employed all day, every day, as a second display for my MacBook. (If you have newer hardware, you may get this for free with Catalina + iOS 13.)
TickTick task manager, closely (very closely) followed by Evernote.
I would be distraught without either of them, on my iPhone and MacBook Air.