Sting is a simple, host-based approach to detecting arp cache poisoning based man in the middle attacks (such as made by ettercap) on your LAN. It uses SNMP to periodically query the arp cache of your router and make sure its entry for you is correct.
SocketSwitchboard is a virtual proxy, router, or VPN. It uses an XML configuration to map incoming traffic on one or more ports to designated hosts and ports on the LAN or on the Internet. It supports complex boolean access restrictions and SSL.