OpenCensus [1] provides an implementation for tracing and app-level metrics, a context wire protocol, and exporters for various backends. While it provides similar tracing APIs to OpenTracing, they're not identical, though there have been some early conversations about resolving this.
I'm the PM for Census at Google, though other vendors are involved as well. Basic implementations for Java and Go are already functional, with much more to come. We gave a small talk at Kubecon last month, but will start promoting the project once it's slightly more mature.