We’ve got some great demos up on the showcases page:
virtualcityMAP: https://cesiumjs.org/demos/virtualcitysystems/
Built on Cesium and 3D Tiles by virtualcitySYSTEMS, virtualcityMAP allows users to publish 3D city maps from CityGML.
ActiveFlight: https://cesiumjs.org/demos/ActiveFlight/
The FAA is using Cesium and 3D Tiles to visualize flight path interaction with multi-layered weather systems based on historical data.
mago3D: https://cesiumjs.org/demos/mago3D/
mago3D is a web based GeoBIM platform built on Cesium that integrates BIM/AEC and 3D GIS.