According to Wikipedia:
- Secure Shell (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Typical applications include remote command-line login and remote command execution, but any network service can be secured with SSH.
An SSH server, by default, listens on the standard TCP port 22. An SSH client program is typically used for establishing connections to an sshd daemon accepting remote connections. Both are commonly present on most modern operating systems, including macOS, GNU/Linux, Solaris and OpenVMS. Proprietary, freeware and open source versions of various levels of complexity and completeness exist.
- Dropbear — Lightweight SSH server. The command-line ssh client is named .
- OpenSSH — Premier connectivity tool for remote login with the SSH protocol
- TinySSH — A minimalistic SSH server which implements only a subset of SSHv2 features; glibc as its single dependency.