This is the example of working plist to run Appium server using launchctl on Mac. See comments for more info and steps how to use this.

com.company.appium.server.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>KeepAlive</key>
	<dict>
		<key>SuccessfulExit</key>
		<false/>
	</dict>
        <key>Label</key>
        <string>com.company.appium.server</string>
        <key>RunAtLoad</key>
        <true/>
	<key>ProgramArguments</key>
	<array>
		<string>/usr/local/bin/node</string>
		<string>/usr/local/lib/node_modules/appium/build/lib/main.js</string>
	</array>
	<key>StandardOutPath</key>
	<string>/Users/path/to/logs/stdout.log</string>
	<key>StandardErrorPath</key>
	<string>/Users/path/to/logs/stderr.log</string>
	<key>EnvironmentVariables</key>
        <dict>
            <key>ANDROID_HOME</key>
            <string>/path/to/android-sdk</string>
            <key>JAVA_HOME</key>
            <string>/path/to/java-home</string>
            <key>PATH</key>
            <string>/content/of/path/env/var</string>
        </dict>
</dict>
</plist>

1. You need to have appium installed using npm install -g appium
2. Copy this file to /Library/LaunchAgents/
3. Run launchctl load com.company.appium.server.plist
   Appium server should start everytime it crashed or system was rebooted.

Thanks for posting this, it worked for me! 👍
Removed the StandardOutPath, StandardErrorPath parts and the EnvironmentVariables part because we use it for iOS only. And simply set:

<key>KeepAlive</key>
<true/>

NOTE: I copied the plist file to the user specific LaunchAgent folder:

~/Library/LaunchAgents

(not to the system folder)
When the plist was placed in /Library/LaunchAgents/ I got errors that the binary for Carthage is not found, missing from the PATH.

After a reboot, you can verify in Terminal if Appium Server is running:
lsof -n -i:4723 | grep LISTEN

thanks for this handy script, but any solution for mirror all system's env variables to launchd?