Nova Launcher update adds adaptive icons, Android 8.1 popup menu, more
Keep in mind that this isn't a beta release, so you'll be able to benefit from all the features included in the update once you download Nova Launcher v5.5.
The most important change is the addition of adaptive icons, which are supported by all devices powered by Android 5.0 Lollipop and newer. Also, the update intelligently reshapes legacy icons to adaptive to come in line with Google's new design language.
There's also a new Android 8.1 Oreo style popup menu, while a new search bar is now available in the dock. Moreover, the new search bar can be replaced in the dock with any widget by simply long pressing on the bar and choosing “Replace.”
Finally, some optimizations and bug fixes have been implemented under the hood, so you should notice some performance improvements and fewer issues with the Android launcher.