Secure tunnels
OpenSSH
OpenSSH is an open-source implementation of the SSH protocol. SSH provides encrypted and authenticated tunnels to carry other protocols across shared networks. The simplest application of OpenSSH is as an encrypted replacement for the telnet terminal protocol, but it can also be used in port-forwarding mode to secure many other communications including access to mailboxes and incident handling systems. Note that version 1 of the SSH protocol has had a number of security problems and users are strongly recommended to use only version 2 of the protocol. OpenSSH supports both versions, as should most other clients and servers.
SSH (Secure Shell)
SSH is a seamless and secure replacement of old, insecure remote login programs such as rlogin or rsh. It has some other features like secure X11-forwarding, port forwarding and a ftp-like secure file transfer subsystem called sftp. Note that version 1 of the SSH protocol has had a number of security problems and users are strongly recommended to use only version 2 of the protocol. OpenSSH supports both versions, as should most other clients and servers.
STunnel
Stunnel is a program that allows you to encrypt arbitrary TCP connections inside SSL (Secure Sockets Layer) available on both Unix and Windows. Stunnel can allow you to secure non-SSL aware daemons and protocols (like POP, IMAP, LDAP, etc) by having Stunnel provide the encryption, requiring no changes to the daemon's code. It requires x.509 certificates, if you want to do it correctly.
