Commonly used as an abbreviated way to say "for real".

Usually used in texting, as many people use as many abbreviations as possible.
It can be a form of agreement towards someone, or disbelief.
If you use it as disbelief you may put a question mark to emphasize that you're asking if they're being serious.

It’s an acronym standing for Can’t Remember A Fucking Thing. It’s usually used to describe embarrassment at being unable to remember someone (CRAFT moment); going onstage as the lead in the latest theatrical performance and your mind goes completely blank (CRAFT situation); the next morning after a night when you got pissed as a fart and woke up in bed cuddling a traffic cone and a string of fairy lights wound round your prick.

"for real" (usually used online. And if used in real life by anyone, stay far away for them.)