s6-networking is a collection of small Unix tools designed to help networking. It includes clock synchronization, Unix and TCP super-servers, Unix and TCP access control, and other miscellaneous utilities. It is particularly suited for management of clients and servers on embedded devices, but works just as well on larger systems.
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.
wwan-helper is a script that establishes a UMTS connection using a Ericsson F3507g Mobile Broadband Module. It was designed to be used with a ThinkPad T420s. It takes care of resetting and reinitializing the modem if the hardware fails to get a WWAN connection, and retries as often as necessary until the UMTS connection is really established. It is meant to run as a hook script for the ifup / ifdown mechanism, but should also work on other networking systems.