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.
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.
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.
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.
Bookling is a simple eBook manager designed to make reading fun. It allows you to store, manage, and read your eBook collection on a desktop computer. It features multiple views for your library, multiple bookmarks, customisable fonts and colors for your book's text, and the ability to store your book collection in your choice of directory. Its back end is cleanly separated from the front end, allowing developers to easily port it to other platforms with a native GTK+ or WPF interface.