FloatingPanel.swift

class FloatingPanel: NSPanel {
	init(contentRect: NSRect, backing: NSWindow.BackingStoreType, defer flag: Bool) {

		// Not sure if .titled does affect anything here. Kept it because I think it might help with accessibility but I did not test that.
		super.init(contentRect: contentRect, styleMask: [.nonactivatingPanel, .resizable, .closable, .fullSizeContentView], backing: backing, defer: flag)

		// Set this if you want the panel to remember its size/position
		//        self.setFrameAutosaveName("a unique name")

		// Allow the pannel to be on top of almost all other windows
		self.isFloatingPanel = true
		self.level = .floating
		self.isMovable = false
		self.backgroundColor = .clear
		// Allow the pannel to appear in a fullscreen space
		self.collectionBehavior.insert(.fullScreenAuxiliary)
		self.collectionBehavior.insert(.canJoinAllSpaces)

//		NSWindowCollectionBehaviorCanJoinAllSpaces and NSWindowCollectionBehaviorFullScreenAuxiliary.
		// While we may set a title for the window, don't show it
		self.titleVisibility = .hidden
		self.titlebarAppearsTransparent = true

		// Since there is no titlebar make the window moveable by click-dragging on the background
		self.isMovableByWindowBackground = true

		// Keep the panel around after closing since I expect the user to open/close it often
		self.isReleasedWhenClosed = true // was false

		// Activate this if you want the window to hide once it is no longer focused
		//        self.hidesOnDeactivate = true

		// Hide the traffic icons (standard close, minimize, maximize buttons)
		self.standardWindowButton(.closeButton)?.isHidden = true
		self.standardWindowButton(.miniaturizeButton)?.isHidden = true
		self.standardWindowButton(.zoomButton)?.isHidden = true
	}

	// `canBecomeKey` and `canBecomeMain` are required so that text inputs inside the panel can receive focus
	override var canBecomeKey: Bool {
		return true
	}

	override var canBecomeMain: Bool {
		return true
	}
}

Usage 
func makePanel() {
		 // Create the window and set the content view.
		 newEntryPanel = FloatingPanel(contentRect: NSRect(x: 60, y: 100, width: 512, height: 80), backing: .buffered, defer: false)

		newEntryPanel!.contentView = NSHostingView(rootView: contentView)

		  // Shows the panel and makes it active
		  newEntryPanel!.orderFront(nil)
		  newEntryPanel!.makeKey()
}