Proto.Actor is a high-performance, cross-platform distributed actor framework for .NET. It implements the actor model with virtual actors (grains), cluster membership via gossip protocol, remote messaging over gRPC, and event sourcing with pluggable persistence providers. The architecture is modular: the core actor runtime (Proto.Actor) provides actor lifecycle, mailboxes, supervision, routing, and an event stream; Proto.Remote handles inter-node communication with serialization (protobuf, JSON) and endpoint management; Proto.Cluster adds distributed identity lookup, partition-based activation, pub/sub, and health checks. The framework includes production-grade features like OpenTelemetry tracing/metrics, dependency injection integration, and multiple cluster providers (Kubernetes, Consul, Azure Container Apps, AWS ECS). Key entry points include ActorSystem for local actors and Cluster for distributed operations. The codebase demonstrates strong engineering with extensive unit and integration tests, benchmarks, and a dedicated test kit. Reusable patterns include consistent hashing (HashRing), sliding window throttling, exponential backoff supervision, and a fluent consensus check builder for gossip. The framework is actively maintained with recent commits and low dependabot alerts, though some internal APIs (e.g., obsolete loggers, CouchbaseNetClient 2.7.x) show moderate technical drift. Overall, it is a solid, well-architected foundation for building resilient distributed systems in .NET.