Lo-PDA

A four-tone handheld that lives on your phone. Hi-PDA's low-fidelity cousin.

中文介绍 / 中文截图 →

Try it: https://nowheremanx.github.io/lopda/ — open it on a phone and "Add to Home Screen".

Lo-PDA is a Progressive Web App styled as a fictional 1986 PDA: a green LCD that shows four tones and nothing else, a D-pad, A and B, SELECT and START on its chin, and a HOME key. It comes with a film camera and a darkroom, a diary, a calendar, a dictionary, a book reader, a pet that lives in the handheld, a four-track tape machine, a cartridge player and a store of small community apps. Everything runs and is saved on the phone. There are no accounts, no ads and no tracking, and it works offline. The app spec is frozen as 1.0, so apps written today keep working.

Shot on Lo-PDA

The camera behaves like a film camera. You load a roll of 8, 12 or 16 frames in one of seven film stocks (Portrait 400, Sunny 200, Verde 400, Pastel 400, Tungsten 800T, Noir 400, Expired). The viewfinder is a live four-tone dither and there is no preview: you don't see what you shot until the roll is developed. A finished roll goes into the darkroom's film box.

In the darkroom each roll is developed once, in colour, with the stock's look, grain, halation, the odd light leak and a date stamp in the corner. The photo viewer is the only place where the LCD shows colour, like a print laid on the glass. Prints leave the handheld as a single print, a contact sheet or a film strip; a roll can also leave as a four-tone negative PNG that carries the colour originals inside, and come back in later.

The seven stocks on one photo, same roll and same development, only the stock changes (the first is the original):

What's inside

Built-in	内置	What it does
Notes	记事本	Opens on today's diary, with "on this day" from earlier years. Tags from #words, search, pins, a trash kept 30 days, a zip of Markdown files out and back in.
Calendar	万年历	Gregorian and lunar calendar with solar terms, 1900–2100, China's public holidays and days off, your own anniversaries. Days with a diary get a folded corner.
Dictionary	词典	English–Chinese, built in and offline (abridged ECDICT). Import StarDict dictionaries; a word book for review; A says the word aloud.
Reader	阅读器	TXT and EPUB books, your own fonts, an e-ink style full refresh. Select text to look it up or quote it into Notes. Two public-domain books included.
Pet	宠物	A small creature that hatches once, gets a name for life and lives in a room on the screen. It eats, plays, sleeps at night, grows up, and some days comes home with a souvenir for its shelf. It never dies.
Tape4	四轨机	A four-track tape machine: drums, bass, chords and melody, 64 patterns chained into a song, swing and tape colour, a mixer, a tape library with four demo tunes, WAV export.
Camera	点阵相机	Live dithered viewfinder, rolls of film, seven stocks, every lens on the phone.
Darkroom	冲洗店	The film box: develop, view in colour, print, export and import negatives.
Cartridge	卡带机	Plays black-and-white Game Boy files you supply, with the chin buttons. Saves can be exported and imported. No games are included.
Radio	电波台	Experimental. Two handhelds talk over sound, like a 1986 modem: both press Link, then send short text and 16 × 16 pictures. Slow on purpose.
Store	应用商店	Install, update and run community apps, by category, with search.
Scripts	脚本	Your own small HTML/JS programs: copy a prompt for an AI, paste the code back, run it in the sandbox.
Settings	设置	Sound, volume, language (中文 / English), which apps may use the sensors and camera, app saves, backup and restore of the whole device, the optional AI line, updates.

The app store

Twenty-two apps today, all open source and all made for Lo-PDA:

Kind	Apps
Games	Paper Tower (a ten-minute tower climb), Fake Yu (a one-key rhythm story), SnapTile (a sliding puzzle from your own photo), Marble (tilt the phone), Candles (blow into the mic), Gomoku (also a two-handheld match over sound), Mole Bop, Gold Dig (a sixty-second hook-and-haul mine), Pagoda (a 3D prologue), Sisyphus (a meditative climb with sixteen lines from Camus), Crossing (spell words on a wheel to fill a crossword), DailyBox (one crate-pushing puzzle a day), Klotski (the sliding-block escape), Foothill (seven days running a mountain diner)
Story	Rain Station, a visual novel with seven chapters and five endings
Tools and toys	Calc and Paint (both preinstalled), Fortune, Kana, Sounds, VecDream, LuckyWay (hold the phone flat like a compass)

Preinstalled apps are ordinary store apps: remove them and they stay removed; the store has them again.

Make an app

An app is one HTML file of up to 512 KB and a manifest.json. It runs in a sandboxed iframe with no network and no storage of its own, and talks to the handheld through a small PAD object:

	What an app can use
Always	The buttons, 256 KB of saved data, named sounds, chip music in MML, custom sound effects, ambience (rain, waves, fire…), the language, PAD.say to speak a line, PAD.dict (words and meanings from the built-in English dictionary)
With a permission	files (export and import one file), motion (tilt and shake), mic (loudness and pitch, never the recording), notes (write into Notes), camera (one four-tone photo through the handheld's own viewfinder), wordbook (the player's own word book), and the experimental link (messages to the same app on another handheld, over sound; Gomoku's match is the example)

Every permission is asked by the handheld itself, not by the app, and the player can say no; apps must still work with the keys. The full rules are in SPEC.md (spec lopda/1, frozen as 1.0: everything in it except link will not change in a way that breaks an app); the screen layout rules are in sdk/UI.md.

cp -r sdk/template registry/apps/my-app       # then edit manifest.json: "id": "my-app"
python3 -m http.server 8086                   # from the repository root
# open http://localhost:8086/sdk/dev.html?app=registry/apps/my-app
node tools/check-app.mjs registry/apps/my-app
node tools/build-index.mjs

• Writing with an AI assistant: sdk/PROMPT.md is a ready-made prompt.
• Games: sdk/lo-game.js has a pixel font, dialogue boxes, menus and tile maps; start from sdk/template-game/, or sdk/template-vn/ for a visual novel. 3D: sdk/lo-3d.js.
• The online harness loads any registry app with buttons and a log, nothing to install: https://nowheremanx.github.io/lopda/sdk/dev.html?app=registry/apps/<id>.
• To submit, open a pull request; CONTRIBUTING.md has the steps in English and Chinese, and docs/REVIEW.md says what a review looks for.

Your data

Everything stays in the phone's browser storage. Settings → Backup writes the whole device (notes, rolls and their colour originals, books, dictionaries, cartridge saves, app data) into one lopda-backup-YYYYMMDD.zip, and Restore puts it back after checking it first. Removing an app keeps its saves; Settings → App saves lists them and clears them, and a reinstall of the same app carries on.

Two things go online, and only these two. The calendar fetches next year's table of China's holidays from jsDelivr when it is missing (the tables up to now ship with the app). And if you add your own OpenRouter key in Settings → AI line (off until you do), Scripts can write a program for you, Tape4 can edit a tape with you and the pet can bring home a souvenir it made up. Each request carries only what it needs (the script you asked for, the tape being edited, the pet's mood and the season), never your notes or photos, and the key is not in the backup. Apps cannot reach the network at all.

Run it locally

Any static file server at the repository root works, because the runtime loads ../sdk/ and ../registry/:

cd lopda
python3 -m http.server 8086
# open http://localhost:8086/runtime/

On a phone, open the runtime over HTTPS and use "Add to Home Screen". Plain http://<your-computer-ip>:8086 works for a quick look, but browsers disable the live camera, offline mode and the share sheet on insecure origins. Two easy ways to get HTTPS while developing:

# a temporary public https URL, no account needed
brew install cloudflared
cloudflared tunnel --url http://localhost:8086
# then open https://<random>.trycloudflare.com/runtime/ on the phone

or publish the repository with GitHub Pages.

node --test runs the test suite (no dependencies). node tools/readme-shots.mjs makes the pictures in this README (it needs Playwright).

Layout

runtime/     the PWA: index.html, core.js, apps/ (one file per built-in), boot.js, strings.js, platform.js, sw.js, fonts, vendor
sdk/         MIT: PAD bridge, lo-game.js, lo-3d.js, templates, dev harness, AI prompts
registry/    index.json + apps/<id>/{manifest.json,index.html}
tools/       check-app.mjs, build-index.mjs, bundle-app.mjs (Node 20+, no dependencies), readme-shots.mjs (needs Playwright)
tests/       run with `node --test`
docs/        decisions.md (why things are the way they are), design notes, review rules
SPEC.md      app specification lopda/1

Design rule

Every change should take a decision away from the user, or at least not add one. Four tones, fixed frame counts, no previews, one development per roll, frames you can't edit. The limits are the point. Why things are the way they are: docs/decisions.md.

The screenshots were made in a desktop browser by tools/readme-shots.mjs (--lang=zh for the Chinese ones), with the camera fed a lake drawn in code. The Radio shot is two tabs of one browser talking through a stand-in for the sound link.

License

MIT. Copyright (c) 2026 Haowei Wu.

Every registry app uses a permissive license of its author's choice. Third-party parts (fonts, the Game Boy core, the dictionary data, the holiday table) keep their own permissive licences, listed in LICENSING.md and NOTICE. The name "Lo-PDA" and its icons are not covered by the license: forks published for others need their own name.