Botan is a crypto library for C++ released under the permissive BSD-2 license.
It provides useful things like SSL/TLS, X.509 certificates, ECDSA, AES, GCM, and bcrypt, plus a kitchen sink of crypto algorithms of various utility. A third party open source implementation of SSHv2 that uses botan is also available. In addition to C++ you can use (parts of) botan from Python or Perl (both included in tree), or with Node.js.
If you need help or have questions, send a mail to the development mailing list. Patches, “philosophical” bug reports, announcements of programs using the library, and related topics are also welcome. If you find what you believe to be a bug, please file a ticket in Bugzilla.