It is this:

PMDG Simulations

Their product is completed to a very high standard. Even all the features of the HUGS work, complete with the parallax of moving your head around, if you are nerdy enough to wear an IR headset while playing flight sim.

Have not bought, or run the thing, but judging from the time, money and effort involved, it's likely mind boggling.

The machine it takes to run it may be also mind bogglingly expensive.

IMHO the 737's flight characteristics would be more difficult than most to model into a desktop sim. The airplane is pretty trim hungry in real life ... which, if modeled realistically, makes it a pain to fly with no tactile feedback what so ever. To a desktop user it would simply seem the thing never wanted to remain in level flight.