Anagram of .com, i guess. Btw, I find myself so many times struggling to decipher abbreviations mentioned in hacker news, can't you people put a short explanation in parentheses whenever you use a not so well known abbr? (that was on purpose)

We should start a pool: How long will it take before the first .cmo domain resolves?

google.cmo doesn't return any hits for me at the moment...