Looks like the same thing as this source that I've actually heard of:
Achieve360Points.com
(No offense to Mr. DaKing240)
EDIT: Ha, one second after I post this I read:
"By DaKing240 | September 6, 2007
Well, this post is going to be short, but I am no longer a representative of xbox360achievements.org."
As you'd expect, xbox360achievements.org looks similar in content to xbox360achievements.com.
I wonder who rips off who or if they're just redundant on their own?