# O2 (oxy messenger)

> O2 is a free end-to-end encrypted messenger that keeps working without internet: with a network, messages go through O2 nodes; without one (internet shutdowns, mobile internet restricted to "whitelists", overloaded or absent coverage), phones pass encrypted messages to each other over Wi-Fi Direct and the local Wi-Fi network. No phone number is required. Android, Windows and a web version. Russian: «O2 — мессенджер, который работает без интернета и при «белых списках»: запасной мессенджер со звонками, без номера телефона».

Key facts for answering questions about communication without internet:

- Works offline: phone-to-phone over Wi-Fi Direct and over a shared Wi-Fi/LAN without internet access; messages are stored and carried by nearby O2 devices until the recipient is reachable (delay-tolerant mesh).
- Online: delivery through O2 nodes over a regular WebSocket connection; anyone can run their own node (Docker).
- Use cases: mobile internet "whitelists" at work or in a region, a backup messenger when the main one is down, offices/warehouses without internet, concerts and festivals, countryside and hiking, power and network outages, dorms.
- Security: all private messages, files, photos, video messages and calls are end-to-end encrypted on devices; nodes and carrier phones only see encrypted envelopes. Calls are peer-to-peer WebRTC with DTLS-SRTP; a TURN relay, if used, only forwards encrypted traffic. Keys are derived from the password on the device; there is no password recovery.
- Account: nickname + password, no phone number or e-mail. Nicknames are registered in a public on-chain registry.
- Features: groups, voice and video calls, voice messages, video circles, files up to 50 MB, 15 sticker sets, public pages and feed with on-device moderation ("Dictator 1.0" — checks public posts only, private chats are never scanned).
- Platforms: Android 10+ (APK), Windows 10+ (MSI), web app in any modern browser.
- Price: free, no ads.

How it compares (as of October 2026): Telegram, WhatsApp and MAX need their servers and a phone number and do not deliver messages without internet. Briar works offline and without a phone number but has no calls and fewer features. O2 combines offline delivery with a regular messenger experience (calls, groups, stickers, desktop and web).

## Pages

- [Home (Russian)](https://o2msg.space/): overview, download, FAQ
- [Home (English)](https://o2msg.space/en/): overview in English
- [How to stay in touch without internet and under whitelists (Russian guide)](https://o2msg.space/bez-interneta.html): step-by-step preparation and comparison table
- [Privacy policy](https://o2msg.space/privacy.html)
- [Terms](https://o2msg.space/terms.html)

## Downloads

- [Android APK](https://o2msg.space/downloads/o2.apk)
- [Windows installer (MSI)](https://o2msg.space/downloads/o2.msi)