A quick click to Natalie Jost's Paper Goods site produced this free downloadable "cardvelope". Just score on two dotted lines (a bone folder works good here), cut on a dotted line for the flap to slip into, then cut around the perimeter of the shape... I used a rotary cutter, and you have a teeny card to write a note on to drop in the mail for some Valentine's Day fun. Natalie shares three different free designs, but this one happens to be my favorite. She also has more cardvelope designs for sale in her etsy shop.