PInvoke.BCrypt by: Andrew Arnott

P/Invoke methods for the Windows BCrypt.dll.

PCLStorage by: Daniel Plaisted

PCL Storage provides a consistent, portable set of local file IO APIs for .NET, Windows Phone, Windows Store, Xamarin.iOS, Xamarin.Android, and Silverlight. This makes it easier to create cross-platform .NET libraries and apps.

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.

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, 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: Claire Novotny

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

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.

QuestPDF by: MarcinZiabek

QuestPDF is a modern PDF generation library for C# and .NET. Create invoices, reports, and data exports — a code-first alternative to HTML-to-PDF conversion. Merge and edit documents, generate PDF/A and accessible PDF/UA files, embed ZUGFeRD and Factur-X invoice XML. Source-available with a free Community license.

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.

PInvoke.Windows.Core by: Andrew Arnott

P/Invoke types for common Windows APIs.