Cilium vs Istio: What are the differences?
Cilium: API-aware networking and security for containers. Open source software for providing and transparently securing network connectivity and loadbalancing between application workloads such as application containers or processes; Istio: Open platform to connect, manage, and secure microservices, by Google, IBM, and Lyft. Istio is an open platform for providing a uniform way to integrate microservices, manage traffic flow across microservices, enforce policies and aggregate telemetry data. Istio's control plane provides an abstraction layer over the underlying cluster management platform, such as Kubernetes, Mesos, etc.
Cilium can be classified as a tool in the "Security" category, while Istio is grouped under "Microservices Tools".
Istio is an open source tool with 18.5K GitHub stars and 3.1K GitHub forks. Here's a link to Istio's open source repository on GitHub.