Istio is an open source service mesh built on Envoy Proxy. Originally created by IBM and Google, Istio provides a broad set of service mesh functionality for managing data center (East/West) traffic, security, and observability. Istio also includes its own ingress controller, the Istio gateway.
Istio is perhaps the most widely known service mesh given its institutional backing. The visibility of the Istio project has helped popularize the service mesh concept.