busybox

Swiss Knife for embed, include a lot of linux cmd (include, vi ,sed, awk, etc)

mbedtls

The Mbed TLS library is designed to integrate with existing (embedded) applications and to provide the building blocks for secure communication, cryptography and key management
learn it @ https://tls.mbed.org/kb/how-to/mbedtls-tutorial
主要用于arm, is for substituting openssl

dropbear

is a ssh server for embed use

musl libc

light weight libc for embed environment

uCore libc