The newest version is the FN 509. Very nice handgun, I like it a lot.
I played around with the 509 but as an existing FNS owner I couldn't see moving off to it. For someone new looking for a duty-sized gun, I could definitely see it though. Just be aware that FNS holsters don't fit it per the FN rep at the NRA show.
As someone who carries an FNS every day, the biggest attraction of the 509 is that Apex is making a trigger for it that will be backwards compatible with the FNS guns...