Polly
Polly is a .NET resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner.
Link: https://github.com/App-vNext/Polly
Otp.net
Useful library for implementing the two-factor authentication
Link: https://github.com/kspearrin/Otp.NET