MediatR

ASP.NET Core

dotnet/aspnetcore

Popular

Microsoft's cross-platform, high-performance framework for web APIs, MVC, Razor and Blazor apps.

Aspire

microsoft/aspire

Rising

Code-first toolkit (formerly .NET Aspire) for orchestrating, configuring and observing distributed apps.

Polly

App-vNext/Polly

Popular

Resilience library for retries, circuit breakers, timeouts and rate limiting in .NET.

FastEndpoints

FastEndpoints/FastEndpoints

Rising

REPR-pattern alternative to controllers and Minimal APIs with high performance and low ceremony.

Orleans

dotnet/orleans

Virtual-actor framework for building scalable, distributed .NET services.

MassTransit

MassTransit/MassTransit

Distributed messaging framework over RabbitMQ, Azure Service Bus, SQS and Kafka; v9 is commercial.

Wolverine

JasperFx/wolverine

Rising

Command bus and messaging framework with a durable outbox, often paired with Marten on Postgres.