Source: Justice Society of America vol.3 #9-22 (2007-2009)
Type: Alternate Earth
Not to be confused with the Kingdom Come Superman, the alternate Earth Superman that joined the JSA for more than a year hailed from Earth-22. Kingdom Come had been tagged as Earth-96 at one point, but could we not say it changed numbers when the multiverse dropped to 52? There are other differences, actually:
-Superman-22 had been retired for less than 10 years, while KD Superman was out of the game for over 15.
-Superman-22 is older than KD Superman. Flashbacks show him with already graying temples when Lois is killed.
-Speaking of Lois-22, she dies differently from KD Lois. The Joker smashed in her skull with a Daily Planet paperweight, while KD Lois was stabbed through the chest with her nameplate.
-Superman-22 arrived before his wife's death, not after.
-Kryptonite still has an effect on Superman-22.
-And of course, KD Superman was not pushed to New Earth by the power of the explosion set off by Captain Marvel like Superman-22 was. When he returns home at the same point, events proceed as in KD.
-Superman-22 has four children with Wonder Woman, two of them girls. KD Superman had only one son.
-The future of Earth-22 shows Superman and WW surviving for hundreds of years. Humanity leaves it for the stars in a hundred years. The planet becomes a waterworld a century after that. New settlements pop up on Earth-22 in 500 years. And an aged Superman-22 lives to see the UFP protected by the Legion of Super-Heroes.
Even so, the history is remarkably similar, and any scene in this Superman's home plane do tend to feature Alex Ross art!
Type: Alternate Earth

-Superman-22 had been retired for less than 10 years, while KD Superman was out of the game for over 15.
-Superman-22 is older than KD Superman. Flashbacks show him with already graying temples when Lois is killed.
-Speaking of Lois-22, she dies differently from KD Lois. The Joker smashed in her skull with a Daily Planet paperweight, while KD Lois was stabbed through the chest with her nameplate.
-Superman-22 arrived before his wife's death, not after.
-Kryptonite still has an effect on Superman-22.
-And of course, KD Superman was not pushed to New Earth by the power of the explosion set off by Captain Marvel like Superman-22 was. When he returns home at the same point, events proceed as in KD.
-Superman-22 has four children with Wonder Woman, two of them girls. KD Superman had only one son.
-The future of Earth-22 shows Superman and WW surviving for hundreds of years. Humanity leaves it for the stars in a hundred years. The planet becomes a waterworld a century after that. New settlements pop up on Earth-22 in 500 years. And an aged Superman-22 lives to see the UFP protected by the Legion of Super-Heroes.

Comments
Siskoid, maybe you've mentioned this, but do you have a favorite Elseworlds?
It's probably The Golden Age, but Justice Riders and Shogun of Steel come pretty close.