BearSSL is an implementation of the SSL/TLS protocol (RFC 5246)
written in C. It aims at offering the following features:

* Be correct and secure. In particular, insecure protocol versions
  and choices of algorithms are not supported, by design;
  cryptographic algorithm implementations are constant-time by
  default.

* Be small, both in RAM and code footprint. For instance, a minimal
  server implementation may fit in about 20 kilobytes of compiled
  code and 25 kilobytes of RAM.

* Be highly portable. BearSSL targets not only "big" operating
  systems like Linux and Windows, but also small embedded systems
  and even special contexts like bootstrap code.

* Be feature-rich and extensible. SSL/TLS has many defined cipher
  suites and extensions; BearSSL should implement most of them,
  and allow extra algorithm implementations to be added afterwards,
  possibly from third parties.

bearssl is considered alpha-quality software, which means that it
runs but it probably has bugs, some of which being certainly
exploitable vulnerabilities.