Embedded TLS Library for Applications, Devices, and the Cloud

See first, mbedtls and openssl with $0 FOSS licensing. Wolfssl needs a 'commercial license' to ship it in a proprietary product:

> Businesses and enterprises who wish to incorporate wolfSSL products into proprietary appliances or other commercial software products for re-distribution must license commercial versions. Commercial licenses for wolfSSL, and wolfCrypt are available for $7,000 USD per end product or SKU. Licenses are generally issued for one product and include unlimited royalty-free distribution. Custom licensing terms are also available.

https://www.wolfssl.com/license/