A million and three years ago, back when I first started creating cards, someone sent me a clever card that was a card and envelope in one. It had flaps that folded shut and a ribbon to secure it closed.
I really liked that design for something different and kept the card for inspiration. The card is so old that it is frayed and faded now but I still keep it to remind me of the technique. Back in those days, I had to trace the inspiration card and cut it out to get the shape made. Nowadays I can use the Envelope Maker to get the shape made perfectly, with rounded corners and all, and I have a variety of sizes I can make.
Even though it is a card and envelope all in one, I put it inside another envelope to mail. I think the post office would frown on the ribbon closure and flower embellishment as well as mangle the card (because that's what they are good at).
So when you are looking for something a little different to make, this is a fun one. And now you know the Envelope Maker trick you don't need to know the dimensions-you can do whatever size you like. This one is roughly 4"x6".
The Fine Print: Since the technique was from 'back in the day' I used a stamp set from that time frame as well--an oldie but goodie by Stampin' Up. Envelope Maker by We R Memory Keepers. I later received a similar card that was secured shut with a sticker, which while nice was kind of hard to open without ruining the card.