American Express lets cardmembers earn points when they refer a friend who applies and is approved for a new card. You’re generally limited only to referring friends and family for cards you already have yourself.
From October 1 through October 28 they’re adding a new bonus to encourage people to refer friends. In addition to the standard points that they’ll give for a successful referral, they’ll also let someone who successfully refers someone earn 3 more points per dollar (or earn 3% more cash back) for the next three months.