being a compendium of resources I've found useful and some historically interesting books

ios books (uikit)

Programming iOS 14	Still the best single-volume overview of iOS.
iOS Core Animation: Advanced Techniques	Everything you always wanted to know about layers.

ios books (swiftui)

Thinking in SwiftUI	A gentle introduction with explanations of what's going on under the hood.
Integrating SwiftUI into UIKit	Practical real-world advice.

swift books

A Swift Kickstart	Concise but meaty.
Swift in Depth	Good advice with good examples.
Advanced Swift	A wide-ranging overview of Swift's more interesting features.

objective-c books

Effective Objective-C 2.0	Best practices and pitfalls.
Objective-C Phrasebook	Surprisingly insightful bathroom reading.
NSHipster: Obscure Topics in Cocoa & Objective-C	Collected wisdom from nshipster.com.

other ios resources

NSScreencast	Weekly videos on iOS development, short and sweet.
Swift Talk	Weekly videos on Swift development, a good mix of theoretical and practical.

macos apps

Araxis Merge	Not the cheapest diff app, but reliable and actively updated.
Attributed String Creator	Generate extremely tedious code for attributed strings.
BetterDisplay	Switch resolutions quickly, including HiDPI modes (and much more).
BetterJSON	Safari extension to prettify JSON content.
BetterZip	View/edit many different compressed file formats, includes QuickLook support.
Bezel	Display your iOS device screen on your Mac desktop.
CodeRunner	Quickly test code snippets.
ColorSlurp	Color palette picker/organizer.
Core Data Lab	An IDE for Core Data.
CustomSymbols	Convert SVG artwork into a custom SF Symbol.
DesktopShelves	Skeumorphtastic shelves for my PDF books/manuals.
ForkLift	Finder for S3 and others.
GeekTool	Monitor log files on the desktop.
GraphicConverter	Sometimes I just want to move pixels around, not layers up and down.
HextEdit	Hex editor.
ImageOptim	Drop-and-drop PNG compressor.
iMazing	Finder for iOS devices.
Integrity	Check website^[sp?] links.
LaunchControl	Edit launchd files. See also lunchy.
MonoDraw	ASCII diagram editor.
Murus	macOS firewall UI.
Pacifist	Extract useful things from un-useful installers.
PaintCode	Generate extremely tedious code for graphic designs.
PastePal	macOS/iOS clipboard manager (yes, I tried all the others).
Patterns	Test regular expressions.
Pixel Winch	A really efficient screen measurement tool.
Postgres.app	Install and manage multiple PostgreSQL versions from the menu bar.
Postico	View/edit PostgreSQL databases.
Proxyman	macOS-native HTTP/S debugging proxy.
RapidAPI	An IDE for web services (formerly Paw).
Reeder	Keep up.
RocketSim	Quick access to Simulator folders and other useful features.
Rotato	Animated iOS device mockups.
Screenflick	Easy screen recording.
ScreenFloat	Quick screenshots.
Sketch	Great vector graphics app.
Stay	Automatically restore windows when connecting/disconnecting external displays.
SwiftUI Companion	Interactive SwiftUI docs.
TablePlus	Polyglot database viewer/editor, great for SQLite.
Typeeto	Combine with Reflector for twice the fun.
Typeface	An improved Font Book.
Typora	Edit Markdown with GitHub styling.
Yoink	A shelf for the Finder.