Which web frame works are free for commercial use?

I am really interested in web development business nowadays.

As you guys know that there are lots of free web frameworks are avaliable.

One thing I have heared from my friends that some of these frameworks are not free if people use them for commercial purpose(such as licence, legal issues).

Is this really true?? If it is true, can you tell me which frameworks are completly free for business?

Thank you.