From Hal2020: http://hal2020.com/2012/09/15/goodbye-forefront-it-was-nice-knowing-you/

Forefront as a business is gone.  The offerings within Forefront have either been absorbed into the Microsoft offerings they were aligned with, into the businesses they were aligned with, or where neither made sense been declared end-of-life.

Forefront TMG (previously known as ISA) was one of the casualties.  This one strikes close to home because it was one of "mine".  TMG was victim to a changing landscape in which the vast majority of the network edge security business had moved to network appliances.  And so TMG was the leading product in the software-only category, but it had become an insignificant factor in the overall market.  In addition, the general view was that the network boundary was going to disappear as the trends toward BYOD, IPv6, and IPsec accelerated.  As such TMG had lost its strategic value before TMG 2010 (which was the major revamp and rename from ISA) even shipped.  It's demise was inevitable, and I knew it couldn't be far off when I saw an article in which Microsoft made available a SNORT rule that Microsoft IT had created.  That meant Microsoft IT had abandoned TMG in favor of a SNORT-based solution.