OpenSSH - A Free SSH Protocol Suite

OpenSSH is the premier connectivity tool for remote login with the SSH protocol. It encrypts all traffic to eliminate eavesdropping, connection hijacking, and other attacks. In addition, OpenSSH provides a large suite of secure tunneling capabilities, several authentication methods, and sophisticated configuration options.

The OpenSSH suite consists of the following tools:

Remote operations are done using ssh, scp, and sftp.
Key management with ssh-add, ssh-keysign, ssh-keyscan, and ssh-keygen.
The service side consists of sshd, sftp-server, and ssh-agent.

Features:

Completely open source project with free licensing
Strong cryptography (AES, ChaCha20, RSA, ECDSA, Ed25519...)
X11 forwarding (which also encrypts X Window System traffic)
Port forwarding (encrypted channels for legacy protocols)
Strong authentication (public keys, one-time passwords)
Agent forwarding
Interoperability
SFTP client and server support in both SSH1 and SSH2 protocols
Optional data compression

OpenSSH is incorporated into many commercial products.

The following operating systems and products are known to integrate OpenSSH into the base system (list is in chronological order, with systems that integrated it first listed earlier).