Ask a friend to sign up to Supernotes, and if they enter your referral code once they've signed up both of you will receive 20 extra cards! You can find your referral code in the User menu, like below:

Note: Misuse of our referral system is noticeable, and will result in withdrawals of all referrals and potential further action.

Have a code, quickly enter it by navigating to the User menu and pressing 'Enter Code':