wolfSSL

Formerly known as CyaSSL, wolfSSL provides an embedded SSL/TLS library aimed at embedded and RTOS environments. It features full client and server support with mutual authentication and can be used on various platforms, as it is very easy to compile.
wolfSSL is designed to deliver extra security without compromising on speed and footprint size. In fact, it is over 20 times smaller than OpenSSL and uses less runtime memory, so you can say it is pretty lightweight. Due to its small size and high speed, it is primarily used in standard operating environments.
The library comes with support for the TLS 1.2 and DTLS 1.2 levels, also offering different progressing ciphers, such as Blake2b, NTRU, ChaCha20, or Curve25519. It uses various public key algorithms, amongst which you can find RSA, NTRU, DSS, EDH, DH, ECDHE-RSA, and more.
The list of supported programming languages includes C, PHP, Java, Perl, and Python. Other features include a Certificate Manager, SSL sniffer support, IPv4 and IPv6 compatibility, stunnel integration, abstraction layers, zlib compression, etc.
wolfSSL comes with support for various chipsets, including Intel, Motorola, STMicro, Microchip, Texas Instruments, and the list is not yet complete. Support for additional chipsets can be added upon request.