When we first started developing Cesium at AGI, we learned that many Cesium developers were already using OpenLayers. For example, over two years ago, Raytheon developed an OpenLayers 2 adapter for Cesium to aid in adding Cesium to Vega.
Likewise, the OpenLayers developers saw significant interest in 3D and Cesium in particular so a goal of OpenLayers 3 was to integrate Cesium. Now, thanks to the work of Camptocamp, Boundless, and Klokan Technologies, OL3-Cesium achieves this. We congratulate them on this development effort and look forward to community collaborations with Cesium and OL3.
Similiar to how OL3-Cesium provides an OL3 adapter to Cesium, WebGL Earth 2 provides a Leaflet-compatible API to Cesium. We're exited to see Cesium at the center of 3D geospatial visualization on the web.