Of the many cool goodies in Google Search, this must be one of the most interesting and useful ones. Simply open Google Now or Google Search in Chrome and look for "bubble level," and you'll get a, well, bubble level. Quite expectedly.
The level appears as the top search card and is interactive. It adapts to whether you're holding your phone in portrait or landscape, or laying it flat on a table. While you may not use this for some very precise work, it is super cool and could come handy if you want to hang a poster or painting and just need an average way to know it's not completely crooked without installing a third-party app.
I was able to test this on my LG G4 running Lollipop 5.1 and Nexus 5X with Marshmallow 6.0.1. But apparently there was an orientation issue in Chromium on Android 6.0 which might stop this trick from working properly on those devices. Give it a try and see how level everything around you is.