Swords & Wizardry begot Crypts & Things and perhaps X-plorers and others.
+Joe D is working an an awesome houseruling of LotFP Weird Fantasy (I've seen it and played in it and it is good). In the end, it I suspect it will be a combination of houserules and setting, more of it's own thing than the rules that it is based on, but time will tell.
I play with a houseruled version of S&W Complete, which is close enough to the core rules that my house rules can fit on a single page.
At what point do houserules stand on their own as a separate set of rules?