PInvoke.Windows.Core by: Andrew Arnott

P/Invoke types for common Windows APIs.

PInvoke.BCrypt by: Andrew Arnott

P/Invoke methods for the Windows BCrypt.dll.

prometheus-net by: andrasm, qed-, lakario

.NET client for prometheus.io

Quartz.Serialization.Json by: Marko Lahma

Quartz.NET JSON Serialization Support

PInvoke.NCrypt by: Andrew Arnott

P/Invoke methods for the Windows NCrypt.dll.

PCLCrypto by: Andrew Arnott

PCL Crypto provides a consistent, portable set of crypto APIs for .NET 4.5, Windows Phone 8.0 SL & 8.1 Xaml, Windows Store, Xamarin.iOS, Xamarin.Android. This makes it easier to create cross-platform .NET libraries and apps. Crypto functionality includes asymmetric and symmetric encryption and signatures, and key derivation. PCLCrypto calls into each native platform's crypto API for maximum performance. For RSA operations this produces a 2-100X improvement in performance on Android and iOS over using the standard RSACryptoServiceProvider API.

PagedList.Mvc by: Troy Goode

Asp.Net MVC HtmlHelper method for generating paging control for use with PagedList library.

Quartz by: Marko Lahma

Quartz.NET Scheduling Framework for .NET Platform

Pkcs11Interop by: Jaroslav Imrich

Managed .NET wrapper for unmanaged PKCS#11 libraries

PInvoke.Kernel32 by: Andrew Arnott

P/Invoke methods for the Windows Kernel32.dll.

Prism.Core by: Brian Lagunas, Dan Siegel

Prism is a fully open source version of the Prism guidance originally produced by Microsoft Patterns & Practices. Prism provides an implementation of a collection of design patterns that are helpful in writing well structured and maintainable XAML applications, including MVVM, dependency injection, commanding, event aggregation, and more. Prism's core functionality is a shared code base in a Portable Class Library targeting these platforms; WPF, Windows 10 UWP, and Xamarin Forms. Features that need to be platform specific are implemented in the respective libraries for the target platform.

Portable.ConcurrentDictionary by: Stef Heyenrath

This is a .NET Standard 1.0, .NET 2.0, .NET 3.5, Silverlight 5.0 and Windows Phone Silverlight 8.0 & 8.1 backport from System.Collections.Concurrent.ConcurrentDictionary as defined in .NET Core

Portable.BouncyCastle by: Oren Novotny

BouncyCastle portable version with support for .NET 4, .NET Standard 1.0-2.0, .NET Core

Plugin.FirebasePushNotification by: Rendy Del Rosario

Receive and handle firebase push notifications across Xamarin.iOS and Xamarin.Android

Plugin.CurrentActivity by: James Montemagno

Provides a simple solution for getting access to the current Activity of the application when developing a Plugin for Xamarin. This will lay down a base "application" class for developers in their Android application with boilerplate code to get them started.

PdfPig by: UglyToad

Reads text content from PDF documents and supports document creation. Apache 2.0 licensed.

Plugin.Permissions by: James Montemagno

Check to see if your users have granted or denied permissions for common permission groups on iOS and Android. Additionally, you can request permissions with a simple cross-platform async/awaitified API.

protobuf-net by: Marc Gravell

Provides simple access to fast and efficient "Protocol Buffers" serialization from .NET applications

Polly by: Michael Wolfenden, App vNext

Polly is a library that allows developers to express resilience and transient fault handling policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner.

QRCoder by: Raffael Herrmann, Shane Krueger

QRCoder is a simple library, written in C#.NET, which enables you to create QR codes.