Top 20 NuGet subscribe Packages

Micro publisher/subscriber library
MailUp Rest API SDK
Lightweight synchronous messagebus for communication within an application.
Event aggregation (Pub-Sub) library for Xamarin and .NET applications. This is basically the MvvmCross Messenger plugin without the MvvmCross part
Utilities for publishing and subscribing to event channels.
Subscribe/Publish events implementation with customizable execution patterns. See https://github.com/Socialtalents/SocialTalents.hp for sources and samples
A multi-threaded in-memory implementation of publish–subscribe pattern.
TCP client API for server maintained at https://github.com/lafreak/go-packet-server