Forword lets you make time capsules, which are basically collections of images, notes, and links (which we try to resolve to embeds).
When you create a capsule you can invite others (by email) to contribute to it, and they have 24 hours to do so. After 24 hours the time capsule seals.
While the capsule is sealed it can't be seen by anybody. It remains sealed for the time period you picked when you created the capsule (1 month, 6 months, or 1 year).
When it unseals all the contributors get notified (again by email) and the get to go back and look at it.