These are business rocks, made from lake stones.
Step 1: Find a Beach or River
Be sure to have permission to take stones if it's on private property, and only take stones from places where you're permitted to.
Step 3: Make it a business rock!
Step 4: Thoughts
One downside is that they don't fit in wallets. An upside, on the other hand, is that no one else has business cards like these!