Interoperating: SSH Sentinel

Popular and well tested.
Sold to SafeNet and subsequently discontinued. Development has ceased.
Also rebranded in Zyxel Zywall.
Also known as Clavister VPN Client.
SSH supports NAT traversal.
There is this potential problem if you're not using the Legacy Proposal option. (FIXME: this link isn't available anymore. Please include the information in the wiki.)
Contains a built-in firewall. Problems reported with XP SP2?

SSH's Sentinel-openswan interop PDF (X.509)
Nadeem Hassan's SUSE-to-Sentinel article (Road warrior with X.509)

Common problems

When tunnel is up no other traffic works.
A: Uncheck the "Deny split tunneling" checkbox (under Policy editor -> VPN connections -> <your_connection> -> properties -> Advanced).

I have installed SSH Sentinel on my computer that already has <some other vpn client>.
A: Most VPN clients for windows hooks into the IP stack in such a way that they can not be installed along side another one. Please have only one installed at a time.

I have extremely weird problems with SSH Sentinel, whats up?
A: There are numerous known problems with SSH Sentinel, make sure you have the latest release (1.4.1 as of this writing). Also check the release notes. (Google for SSH Sentinel 1.4.1 Release Notes)