Top 20 NuGet interface Packages

Provides interfaces for implementing a base DAL entity, base DAL mapper, base CRUD repository and base unit of work class
Provides interfaces for implementing base classes of entities, mappers and services on BLL-level.
FlagConsole is a library for .NET, written in C#, which helps to build text-based console application interfaces. It provides controls like panel, textfield, list view, menu, rectangle, line, and label.
Interface for enabling a class to expose his unique identity. Generally a primary key.
Advanced Windows Forms controls
Core interfaces for Reimers.dk Libraries
The Polaris Common Infrastructure contains elements that are shared among multiple Polaris feature packages. By supplying a set of contracts and commonly used functionality to all the feature packages, the Common package permits a losely coupled architecture
An easy way to run command line tasks for any .Net project. Add a CLI to an app in seconds.
A set of classes for working with IBM i data in C# .NET. NOTE: This version requires Client Access 6.1. Please download the source at https://github.com/MikeWills/IBM-i-.NET-Interface to compile to other versions.
Scaffold code generator for generating wrapper class to any existing non-testable classes such static classes and .Net libraries like System.IO. Very useful for doing TDD and decoupling dependencies to 3rd party libraries. Usage: On Package Manager Console type the following command: ...
Base Library for Developing T4SQL Templates Library Add-ins. See detail in http://t4sql.codeplex.com
.NET library that allows you to create types at run-time using an easy-to-use Fluent API that looks like Basic code.
Generic interfaces
Abstraction for cpodesign nlogger implementation
FrameworkAbstraction provides wrapper interfaces around .NET framework classes which interact with the operating system (e.g. classes in the System.IO.File and System.Net.Sockets namespaces). This allows for mocking of these classes in unit tests.
The presentation user interface library for the "More" framework.
Instead of hooking up on EPiServer DataFactory events, simply make your page type implement an interface.
Console Shell for .Net
A library to enable simple multi-pane console applications
Provides "More" patterns and practices for hosting Microsoft ASP.NET applications.