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.
BetterZip	View/edit many different compressed file formats, includes QuickLook support.
CodeRunner	Quickly test code snippets.
ColorSlurp	Color palette picker/organizer.
Core Data Lab	An IDE for Core Data.
DesktopShelves	Skeumorphtastic shelves for my PDF books/manuals.
Faux Pas	Objective-C Xcode project analyzer.
ForkLift	Finder for S3 and others.
GeekTool	Monitor log files on the desktop.
gfxCardStatus	Why do I only have fifteen minutes of battery left?
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.
Kite Compositor	Generate extremely tedious Core Animation code.
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.
Paste	macOS clipboard manager (yes, I tried all the others).
RapidAPI	An IDE for web services (formerly Paw).
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.
Reeder	Keep up.
Reflector	Display your iOS device screen on your Mac desktop.
RegExhibit	Test regular expressions. Free and open source.
ResolutionTab	Switch resolutions quickly, including HiDPI modes.
Reveal	Why does this view overlap that view?
Rotato	Animated iOS device mockups.
Screenflick	Easy screen recording.
ScreenFloat	Quick screenshots.
Sim Genie	Quick access to Simulator folders and other useful features.
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.
Vernissage	App Store screenshot editor.
Yoink	A shelf for the Finder.