The A/F-X (Attack/Fighter X) was a joint USAF/USN project to produce a
heavy attack aircraft with a secondary fighter role; it would have replaced
the F-111 and A-6 in the attack role, and (partially) the F-14 in the
fighter role.  It was a short-lived programme, originating in 1991 after
the cancellation of the McDonnell Douglas/General Dynamics A-12, a highly
advanced, highly stealthy aircraft intended to replace the A-6.  A new
programme, originally designated A-X, was initiated to provide a cheaper
A-6 replacement.  At the same time, the NATF (Naval Advanced Tactical
Fighter) programme, intended to produce an F-14 replacement, had recently
been put on hold, and the USAF was starting to think seriously about an
F-111 replacement.  The three programmes were merged under the title A/F-X.

The leading contender was the Lockheed/Boeing AFX-653, essentially a
navalised version of the USAF's F-22 Advanced Tactical Fighter (see below).
This would have been a two-seat aircraft with Tomcat-like swing wings, but
otherwise similar to the F-22.  The A/F-X project was cancelled at the end
of 1993; the US Navy intends to procure the F/A-18E/F series as partial
replacements for its aircraft.  Lockheed and Boeing are still working on
the AFX-653, and hope to offer a further developed version for a future
project (but probably not JAST (see below), for which the AFX-653 would
probably be too big).

You can find an article on the subject, with plans of the AFX-653, in the
26-Jan-94 issue of _Flight International_.

Vital statistics (AFX-653):  power plant:  two 113 kN Pratt & Whitney
PW7000 augmented turbofans; armament:  one 20mm cannon, internal bays for
various air-to-air and air-to-ground weapons, including AGM-86E missiles
and GBU-24 guided bombs.