Tessera
A letter, waiting for its day.
Tessera is a tool and an open format for writing letters meant to be opened years or decades from now: to a child at eighteen, to yourself at sixty, to a stranger in 2126. You write in a plain-paper room that never leaves your device, then seal the letter into a folder of files and a matching print kit. Sealing generates a hospitality token, cut in two: one half stays with you, the other travels with the letter, so that decades later the matching halves confirm it's real.
Nothing about Tessera depends on a company staying in business. The format is public domain: one letter, one folder of plain text files, readable with nothing but patience. The tool is a static page with no build step and no dependencies, easy to fork or mirror. No accounts, no cloud storage of your letters, no delivery service promising to email your future self.
It's built in the open, one version at a time, and most of the roadmap is now live. As of v0.7 you can write, seal, and print a letter, open and verify one you were sent, set a reminder that needs no server, lock a letter behind a passphrase, co-write one with a second person, and bind a set into a printable booklet. What's still ahead: a shared commons, and an optional cloud save that keeps paper as the reference copy. The repo is public under a source-available, noncommercial license: look, learn, and run it yourself, though a commercial edition is a separate matter.
A quiet, distraction-free composer that runs entirely on your device. No account, no server. Drafts autosave to localStorage and the page works offline via a service worker.
One action produces two things: a folder of plain files (the letter, a machine-readable manifest, a self-describing README, checksums, the token art) and a print kit typeset for paper: cover sheet, opener instructions, token sheet included.
Named for the tessera hospitalis, the token ancient hosts broke in two so descendants, strangers to each other, could reunite the halves and be recognised. Every sealed letter generates one: a deterministic two-half SVG, one half kept, one half travels with the letter.
A calibration corpus of prompts for the letters that matter most: written for a specific bad night rather than a date: open when you're sad, when you doubt yourself, when it's 3 a.m. and you can't sleep.
A local, on-device ledger of every letter sealed, with a printable register page. No account, no cloud, nothing that outlives the machine unless you print it.
Receiving is built too: open a letter meant for you, verify its token halves match, and read it. Reminders export as a plain calendar file, and a passphrase can keep a letter sealed until its day.
The print kit contains everything a letter needs; the digital folder is convenience. Tessera is honest that no cryptography can stop someone opening an envelope early. Custody and care do that, the way they always have.
The spec is CC0: public domain, forever. One letter is one folder of plain text, legible in 2126 without any particular software. The tool itself is a static page under a source-available, noncommercial license: no build step, no npm install, forkable to a USB stick.