Mobster's ROM is really smooth because of various performance tweaks and overclocking. But Project Butter isn't just an apk that you can install on an ICS ROM; it's a project that was done for Android 4.1 to improve smoothness. So it's integrated into Jelly Bean.
Mobster's ROM might do some of the same things that Jelly Bean does to improve smoothness, but as far as I know it's impossible to advertise any ICS ROM as having Project Butter.
Since it's an Android 4.1 ROM, CM10 has it, and yes, it's smooth.