Top 20 NuGet environment Packages

Preflight Client API
Preflight Push Model
description of Infra.Environment
Library meant to provide easy abstraction and mockability for common .NET classes (e.g., DateTime, File, Environment).
A tiny helper framework for providing environment-specific app/web.config configurations, and other configuration utilities.
Environment functions (such as device name) for cross platform development on Android, iOS and WinRT
A lightweight library to load application configuration settings into a dictionary.
Naval Simulation (NavySim) Foundation Library (NFL)
SimpleBlackboardConnect is a .NET Core class library that can be used to connect to Blackboard to obtain the Access Token to integrate your application with Blackboard and make API calls for CRUD operations. Visit the project site to get more info on usage.
Module to allow environment specific styling (and text) on login screen and header ribbon for Sitecore 8+
Allows encoded environmental configurations
Easily manage configuration within your .net application
Library for reading configuration from multiple sources in .NET. Current sources are in memory properties, app settings file, environment variables and command line arguments. It is also possible to implement your own configuration sources (like database, consul, etcd, etc.)
Contains testing utilities for Spectre.System.
A library containing cross platform abstractions for environments and IO.
Proteus.Utility.Configuration is a library that abstracts reading config values from e.g., app.config/web.config and supports their being overridden by ENVIRONMENT VARIABLES and/or a local.settings.json files.
Ms Windows Process infra structure - Windows runtime processes environment libraries
Enver is a helper library that populates properties on your classes from environment variables that you define.
Environment Settings should live in Environment Variables. Not XML! Not on Source Code!
A library of general types for many common uses pertaining to the configuration of any .NET project.