On Apple's OS X SLADE can be installed using Homebrew package manager.

Prerequisites

This guide assumes that you are using the recent version of OS X, like Mavericks or Yosemite. Particular combination of older versions of OS and development tools may require additional actions.
The earliest supported version of OS X is Lion.
For instance, some versions of Xcode don't install Command Line Tools by default. You need to configure it by hand.

How to install

Start from the fourth step if you already have Homebrew installed. But first, check the important note below.

1. Install Xcode from Mac App Store. If you have a developer account, you can also install it from Apple Developer website.
2. Start Xcode, accept its license agreement and enter your password to finalize the installation process.
3. Install Homebrew. It's likely that you need to enter your password once again.
4. Start Terminal.app.
5. Execute brew doctor command to verify Homebrew operation. It should output something like Your system is ready to brew. If it's not the case, carefully read messages and follow proposed actions.
6. Execute brew tap alexey-lysiuk/slade command to add SLADE formula.
7. Execute brew install --HEAD slade command to install SLADE. This step will take a while.
8. Execute brew linkapps slade command to add SLADE to Applications folder.
9. Start SLADE from the Launchpad or directly from Applications folder.

How to update

1. Start Terminal.app.
2. Execute brew update command to update Homebrew to the latest version.
3. Execute brew upgrade slade command to update SLADE to the latest version.

Wait, I want to debug!

Just a warning: You must have some experience with Xcode and programming in general to do so.

1. Complete all installation steps.
   • If you are on Yosemite or higher you will need to build wxWidgets against the LLVM C++ Standard Library (libc++). When configuring wxWidgets, try ../configure --enable-debug --with-macosx-version-min=10.10
2. Clone SLADE repository using your favorite Git client or simply from the command line: cd && git clone https://github.com/sirjuddington/SLADE.git.
3. Generate XCode project using CMake.app. Use ~/SLADE as a source code path, and ~/SLADE/release as a binaries path. Press Configure button, wait for process to finish, then press Generate button. If you don't have CMake.app installed, use cd SLADE && mkdir release && cd release && cmake -GXcode .. command.
4. Open XCode project located in SLADE/release folder, from the Finder or by using open SLADE.xcodeproj command.
5. Build and run SLADE by pressing Command + R.

Next time, when you want to grab the latest SLADE source code, do the following:

1. Pull from SLADE repository using your favorite Git client or use cd ~/SLADE && git pull command.
2. Update XCode project using CMake.app, i.e. press Configure, wait, press Generate. Or from the command line: cd release && cmake -GXcode ...
3. Open XCode project and run as usual.

Important note for Homebrew users

At the moment of writting, wxWidgets formula cannot be used to build SLADE. Use brew info wxmac command to check the status of wxWidgets. If it's installed, you need to execute brew unlink wxmac command, because SLADE installation will fail otherwise. Hopefully, this will be fixed with the next release of wxWidgets.