When saved as an Automator workflow service in OS X, this Applescript will toggle the visibility of the character viewer palette. This is useful in older versions of OS X, which didn't provide easy access to special characters like emoji, etc. I bound this workflow to the Command-Option-Control-C key press for easy access.

Toggle Character Viewer.workflow

on isRunning(applicationName)
	tell application "System Events"
		set appNameIsRunning to exists ¬
			(processes where name is applicationName)
	end tell
	
	return appNameIsRunning
end isRunning

on run {input, parameters}
	if isRunning("CharacterPalette") then
		tell application "CharacterPalette" to quit
	else
		-- tell application "CharacterPalette" to activate
		tell application "Finder" to open item "System:Library:Input Methods:CharacterPalette.app" of the startup disk
	end if
	
	return input
end run