rfc3394 is a C# implementation of the RFC 3394 key-wrapping algorithm. The associated assembly provides two simple operations: one to wrap key data, and another to unwrap the key data. This code also includes a fairly comprehensive unit test library which, among other things, ensures that the implementation is verified against the test vectors provided in RFC 3394.
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.
Lasso (Liberty Alliance Single Sign On) is an implementation of the Liberty Alliance specifications. These specifications define protocols for federated identities, single sign-on, etc. Lasso supports ID-FF 1.2, SAML 2.0, and parts of ID-WSF. It provides both a C library and bindings for several languages (Python, Java, Perl, PHP 4, and PHP 5).