Nextcloud development environment on macOS
(If you use macOS 10.12 Sierra or earlier, you also need to install dependencies: Get php71 and sqlite via Homebrew.)
Get Nextcloud submodules: Using the Terminal, run this command in the nextcloud folder you just cloned:
git submodule update --init
Start the server: In the Terminal, run the command:
php -S localhost:8000
Finish installation: In your browser, go to http://localhost:8000. You should see the setup screen asking for username and password.
(Special thanks to @xMartin for his quick start guide!)