Wikipedia
WolfSSL
wolfSSL (formerly CyaSSL or yet another SSL) is a small, portable, embedded SSL/TLS library targeted for use by embedded systems developers. It is an open source implementation of TLS (SSL 3.0, TLS 1.0, 1.1, 1.2, and DTLS 1.0 and 1.2) written in the C language. It includes SSL/TLS client libraries and an SSL/TLS server implementation as well as support for multiple API's, including those defined by SSL and TLS. wolfSSL also includes an OpenSSL compatibility interface with the most commonly used OpenSSL functions.
A predecessor of wolfSSL, yaSSL is a C++ based SSL library for embedded environments and real time operating systems with constrained resources.