ISA Server 2006 was unconfined on 17 October 2006. It was an reorganized description of ISA 2004, and retained most features. One disparagement of all Microsoft ISA server edition to date, is the lack of resident support for a "fail-over" or secondary WAN connection. This would facilitate two (or more) separate network interfaces, to be configured to two divide ISP, allowing leverage of multiple cheap ADSL connections and failover.
ISA Appliance Edition
Microsoft as well suggest what they call ISA 2006 appliance version, software intended to be pre-installed onto a OEM server, and trade by the hardware manufacturer as a stand alone firewall type device.