ENet for C# wraps the C-language ENet networking library. For games and other realtime applications, if you use TCP, old data can hold up newer data, even if it is no longer relevant (old positions, etc.). Your players will perceive any lost packet as a "lag burst". ENet supports multiple in-order streams of data, and allows you to decide on reliability on a per-packet basis. The library is useful for both client-server and peer-to-peer architectures.
CryptSharp provides a number of password crypt algorithms: BCrypt, MD5 (and Apache's htpasswd variant), PHPass (WordPress, phpBB, Drupal), SHA256, SHA512, and Traditional and Extended DES. It also includes Blowfish, SCrypt, and PBKDF2 for any HMAC (.NET's built-in PBKDF2 implementation supports only SHA-1). If you are looking to store passwords, odds are CryptSharp will have the algorithm you want.
NetIRC2 is an easy-to-use .NET IRC client library. It supports all major features relevant to making a chat client or bot. It has full support for synchronization contexts. You can use it from a Windows Forms or WPF GUI thread and chat events will be automatically dispatched, allowing you to completely ignore multithreading. It uses byte arrays internally, so mixed encodings can be handled. The IrcClient class can even be used as a component in the Forms Designer. Because it speeds up connect times with some IRC servers, an Ident server is included as well.
LibLogicalAccess is an RFID library developed in C++ for Linux/Windows, also available on C# for use on Microsoft operating systems (using a COM wrapper). It provides low-level commands access and high-level generic abstraction for several chips and readers (PC/SC readers like OMNIKEY, STid readers, etc.) on 125Khz (EM4102, HID Prox, etc.), 13.56Mhz ISO14443/ISO15693 (Mifare Classic, Mifare DESFire, HID iClass, etc.), and 433Mhz frequencies.
Playtomic is a set of client and server APIs for game leaderboards, user generated content, and dynamic updates. It began as a hosted service providing tools and analytics for game developers, but is now available for developers to operate on their own. It includes the API server which is written in NodeJS and backed with MongoDB, along with game client APIs for HTML5, Flash, iOS, Android, Windows, and Unity3d games.
Zyan Drench is a simple yet very entertaining game developed using the Zyan Communication Framework. The Game board is a random picture of size 15x15. Start from the top-left corner of the board. Select a new color for the top-left pixel, and all adjacent pixels of the same color will be painted over with the new color. The goal is to drench the whole board with your own color. Zyan Drench has several modes: play against Android phone (with adjustable skill level), play solo (classic single-player mode), and network game. It is completely ad-free and open source.