Mac OS X

A popular theme for Windows.

I used to have Mac OS X as the theme of Windows XP. Now that I’m using Windows 7 and it’s not needed anymore.

ACM

An abbreviation for the Association for Computing Machinery, the world’s largest professional society in computing. It has a large number of publications has a great digital library.

Not to be confused with AC Milan.

How am I supposed to come up with an example for ACM...?