Before Istio became synonymous with a service mesh, this field was represented by Linkerd. There is some confusion regarding the naming, as the original Linkerd project was designed to be platform-agnostic and targeted the Java VM. This meant that it was resource-heavy and often sluggish. The newer version, called Linkerd2, has been rewritten to address these issues. Linkerd2, as opposed to the original Linkerd, is only focused on Kubernetes.
Both Linkerd and Linkerd2 use their own proxy solution instead of relying on an existing project such as Envoy. The rationale for that is that a dedicated proxy (versus a general-purpose Envoy) offers better security and performance. An interesting feature of Linkerd2 is that the company that developed it also offers paid support.
