SSL/TLS Implementations

Botan

Strictly speaking, Botan is a general-purpose crypto library, but has a TLS implementation. Source is kept in Monotone, but there is a Github mirror. Botan has had continuous development since 2001. Is it safe to use in a commercial product? Good question.

It builds on Unix/POSIX and Microsoft Windows. There are instructions for both iOS and Android builds referenced in the documentation.

Reference

Wikipedia - Botan
SSL implementations compared - although this is really about coding style.
Stack Overflow - Looking for a High Level C++ SSL Library
Speedtest and Comparsion of Open-Source Cryptography Libraries and Compiler Flags - by the author of CryptoTE.
SSL and TLS - sample from old Botan manual
Botan’s Implementation of the McEliece PKC - cryptography resilient against quantum computers?
Building the Botan library for ios7 arm64

OpenSSL

Reference

LibreSSL

LibreSSL is a fork of OpenSSL done by the OpenBSD folks as a security-focused rewrite. There is a new library coming called ressl, for reimagined SSL.

LibreSSL

goreSSL

Schannel

Secure Channel or Schannel is the name of Microsoft’s SSL implementation, implemented as an SSP in their Security Support Provider Interface.

Reference

Secure Transport

Secure Transport is Darwin/Mac OS X’s name for SSL. Modern features are only supported in Mac OS X 10.8 or later. Also annoyingly, you must put certificates in the Keychain instead of bundling them with your program. But it’s open source under the APSL 2.0 license.

Secure Transport Reference