Dark Mode in macOS Mojave is a great new feature, but Apple didn't give us a way to quickly switch between light and dark modes. The little donation-ware app NightOwl gives you that control in your menu bar. You can also set a keyboard shortcut, select apps to stay in light mode, and set specific times to switch between modes.
A little-known trick will allow you to run your Mac's screensaver as a desktop background. You can use this to have an animated desktop, display useful information, or just for fun. It could be useful in situations where you have your Mac just playing music in a shared space and want something more interesting being shown than just a static image.