A tato is a Japanese container that lies flat. They tend to be symmetrical. Letter folds are meant to contain a message, and envelopers are containers that are usually sealed after use. Tatos are meant to be reusable. Through the ELFA mailing list and my own research I have found how to build tatos for three to eight-sided regular polygons. Most instructions for a triangle start from a triangular piece of paper. I found a way to do it from a square.
I created this envelope fold a couple years ago while playing around with folding in thirds. It is not the most elegant envelope, but I can can truly say it is my own creation. All too often after discovering an envelope fold I find it already documented somewhere else months later. After sharing this with the ELFA mailing list, no one has mentioned any similar models.
Yami Yamauchi has an Origami model called "Jacob's Ladder". There is a variation called the "Magic Wallet", but I found the instructions to be complex and the final piece allows the contents to slip out. I've revised the model to add a pleat to the top and bottom so contents are held securely in place. I've diagrammed the revision, which I'm calling "Jacob's Ladder Envelope". The diagram shows how to build the envelope with 8.5 x 11" paper to perfectly hold credit-card sized objects. This revision is also thinner, has nicer looking edges, and introduces two new pockets to the outside of the envelope.
Please try it out and and share your experiences. I appreciate any feedback. I've uploaded a video of myself demonstrating the envelope to YouTube.