You can share and join cards on Supernotes in multiple ways, one of these is by generating share link(s) for a card. This creates a secret url, so anyone with the link can view the card – even if they don't have Supernotes!
How to create a share link?
You can generate a new share link in the 'Sharing Options' of a card (third icon along the bottom).
You can create multiple share links, each with varying permissions, allowing people to only view the card or be able to join the card with a certain role (reader, contributor, editor, and moderator).
At any time you can delete a share link, and this will remove the card from that url (caution: you won't be able to get that share link back, so be careful!).
How private / secure are share links?
Share links are based on a code comprised of four randomised English words like so,
Books Plane Phone Letter . And before you say 'that doesn't sound very secure...' – it results in an incredibly secure code, that would take current computers 185 years to crack (at 1000 guesses per second).