One of the big Qs from pundits before the DMA was ‘what are all these 'great' apps we're missing out on because of Apple's App Store restrictions, and do they even exist?’.
Mere days after a major App Store rules change, @delta (which has been denied for years), is the top app on the App Store.
For every Delta, there are a thousand great apps that were simply never started because they would never fly. Dreams that never left the whiteboard, market segments that were never given chance to exist
Some simple categories of apps that can't realistically exist on the iOS/iPadOS/visionOS App Store off the top of my head (there will be rare, hoop-jumping exceptions, of course):
• Virtualization tools & VMs
• Emulators or language runtimes that require JIT
• Compilers & IDEs that can deploy locally
• Disk management tools
• Backup and recovery software
• Screen sharing & remote control
• Any software with a plugin model for extensibility (like most pro apps)
• System shell replacements
Many of Apple's apps, like Playgrounds, simply could not be built by *any* third party developer.
Playgrounds uses all kinds of special entitlements, JIT, and system access so that it can compile apps using Swift, run them locally, and deploy them to the homescreen. An insurmountable competitive advantage vs any other third-party developer tool on the platform.
(And Playgrounds is provided for free, which makes it pretty hard to compete with even if you did have all the same features)
If you want to talk about walled garden lock-in, Playgrounds goes full circle:
It is the only real developer tool you can use on iOS and it only supports Swift. So it (intentionally or unintentionally) leverages Apple's market power to juice Swift and SwiftUI (at the expense of any other language or development environment), which leads you as a learner straight into Apple development, the App Store, Apple's ruleset, yearly account fees and giving 15/30% of your future revenue to Apple
@stroughtonsmith only Apple could make the playgrounds safe
@stroughtonsmith It's very generous of you to say that this may be unintentional 
They know exactly what they're doing
@stroughtonsmith Killing the App Store monopoly and forcing open Apple's mobile OSes would be letting a million flowers bloom. We'd have to look back after a decade or more to fully appreciate the results.
@stroughtonsmith This is true-ish but Codea significantly predates Playgrounds, as does Pythonista. Bringing code into them has been hobbled at a lot of turns and your points about lock-in/funneling remain, though I question how many people come to playgrounds not already determined to code for Mac/iOS.
@stroughtonsmith looking at my Vision Pro screen. What is Playgrounds?
@stroughtonsmith Apple seems very welcoming to new developers until you get to App review (after you’ve put in all the work). Once you’re on the store the annual fees to stay there pushed me at least right back off.
@stroughtonsmith There’s no “unintentional” with Apple or any other giant tech company.
@stroughtonsmith Even a simple Dynamic Island timer like in Clock can’t be replicated well!
I thought maybe I could get away with live activity notifications, but nope! Need a server to do that… and somehow others will suggest that with a “it’s easy." I don’t recall the system timer not alerting if one loses web connection! 
Ex: Building a rest timer into my workout app was a pain. It’s quite obvious this constraint was intentional, as it’s the same fking notification api to update remotely!
@stroughtonsmith Yeah, imagine doing something like HyperCard, RealBASIC or VB: Teach people programming, and let them share what they made with their friend. Not possible right now.
@uliwitness @stroughtonsmith so much this! HyperCard decks you could share would still be amazing, 20 years late, but amazing
@stroughtonsmith As someone who has built tools like that (processing.org), it drives me insane that it's not possible for a third party to really build something like Playgrounds. Such an incredible waste.
And having used the Mac since the original 128K, I've watched how Apple's dev tools have always been outdone by third parties (Lightspeed C vs MPW, later Metrowerks, etc…) and it's frustrating that they lock down their platform this way.
(Interface Builder, as inherited from NeXT was briefly an exception, but it's long since outlived its usefulness.)
@stroughtonsmith most external usb devices
@stroughtonsmith Torrent clients
@stroughtonsmith • Clipboard Managers
• Window Managers
• Spotlight alternatives
Not just new categories. Old ones, too. At the time when I was using Halide I was constantly peeved I cannot set it up as my default camera.
Apple will continuously revert to playing Apple Music (or showing it in CarPlay) instead of Spotify.
Perhaps "you must let people set defaults" from DMA coupled with new app categories will disrupt this swamp
@stroughtonsmith
@siracusa described it once on @atpfm well, too. For example anything that changes or replaces system interaction behavior. Something like Stage Manager cannot be created by the community, even though they might have fantastic ideas.
@stroughtonsmith better/more backup options would be quite nice.
@stroughtonsmith • Automation or Workflow tools.