OpenChat is a free, open-source chat client for Windows that runs on the Nostr network and implements the Marmot Protocol for end-to-end encrypted group messaging. It suits people who want private group conversations without handing their messages to a central company that can read or store them.
The program is built around MLS (Messaging Layer Security, RFC 9420), a standard designed for group encryption that also provides forward secrecy, so that compromising a current key does not expose earlier messages. OpenChat is released under the MIT license and is written in C#/.NET. Note that the project's latest code update is dated October 2026, so check the official releases page for the newest build before installing.
What Is OpenChat and How Does Nostr Fit In?
OpenChat is a client, meaning the program you run on your computer to read and send messages. The messages themselves travel over Nostr, an open protocol in which users publish signed events to relay servers. Anyone can run a relay, and no single operator owns the network.
Because identity on Nostr is a cryptographic key pair rather than an account on a company's server, the usual idea of a sign-up form does not apply. Your public key is your address, and your private key proves that you wrote a message. This is why the login options in OpenChat revolve around keys.
That design gives users more control, but it also means that losing a private key can mean losing access to an identity. Treat your key as you would a password manager master key: back it up somewhere safe and never share it.
Who Is OpenChat For?
OpenChat suits people who already use Nostr or want a private messaging tool that does not depend on a central platform. Small teams, communities and friend groups that care about who can read their conversations are the natural audience.
It is also useful for developers and cryptography enthusiasts. The project is open source under the MIT license, so you can read how MLS group messaging is implemented, compare the Rust and C# backends, or adapt the code for your own Marmot-based application.
If you need a polished, mainstream chat experience with features such as large public channels and familiar account recovery, a centralized messenger may fit better. OpenChat rewards users who accept a little extra setup in exchange for stronger privacy guarantees.
Why Group Encryption With MLS Matters
Encrypting a one-to-one conversation is relatively simple. Encrypting a group is harder, because every member needs keys that stay in sync as people join and leave. MLS, the Messaging Layer Security standard described in RFC 9420, was designed specifically to solve this problem efficiently.
Forward secrecy is the property that makes MLS attractive. If a device is compromised today, keys from earlier in the conversation should not let an attacker decrypt the history. Rotating keys as the group changes helps achieve this.
In practice, the benefit shows up when a member leaves a group: the remaining members can continue with fresh keys that the departed person does not hold. This is a meaningful improvement over sharing one static password across a chat.
Practical Scenarios for Private Group Chat
Consider a small volunteer organization that wants to coordinate privately. Members can create a Marmot group, share files such as meeting notes, and send voice messages when typing is inconvenient. Reactions keep quick acknowledgements lightweight.
A freelance team working across time zones might use the direct messages for one-to-one questions and the group for project updates. Because each conversation is encrypted, sensitive client details do not sit in plain text on a third-party server.
A developer experimenting with Nostr could run OpenChat alongside other clients to test how messages, relays and encryption interact. The Docker option listed among the platforms makes it easier to run supporting components in a controlled environment.
Key features
Encrypted Marmot group chats
Direct messages with NIP-44
Voice messages
Encrypted image and file sharing
Emoji reactions
Flexible login with Amber or a local key
Desktop and Android
Two MLS backends
Interoperability
Runtime theme switching
Supported coins
OpenChat is a messaging client rather than a wallet or trading tool, so it does not handle coins. The only network it is documented against is Nostr, the protocol that carries its messages.
How to install OpenChat on Windows
- 1
Get the program from the official source
Download only from the official website or the project's GitHub Releases page at https://github.com/DavidGershony/openChat/releases. Choose the Windows build or installer for the latest version, which is listed as v0.7.9.
- 2
Verify the download
If the release page publishes a SHA-256 checksum or a signature for the file, compare it with your download using a tool such as PowerShell's Get-FileHash before running anything. A mismatch means the file should be discarded.
- 3
Run the installer
Open the installer and follow the prompts. Windows may show a SmartScreen warning for unsigned or newly published software; confirm the file came from the official releases page before continuing.
- 4
Create or import your identity
On first launch, decide how you will sign in. You can connect the Amber signer with NIP-46 so your key stays outside the app, or paste a local nsec key. Back up whichever key you use before joining any group.
-
Connect and start chatting
Once signed in, you can open direct messages or create a group. Keep your relay configuration in mind, since the messages you send will be published to the relays the app uses.
How to use OpenChat
OpenChat is straightforward once your identity is set up. The sequence below covers the typical first session, from sign-in to sending encrypted media.
- Launch OpenChat and sign in with Amber over NIP-46, or enter your local nsec key.
- Confirm your public key is shown correctly, so others can find and add you.
- Start a direct message by entering the other person's public key, or create a new Marmot group for several people.
- Invite members to the group so that MLS can set up the shared encryption state for everyone involved.
- Send a text message, then try a voice message by recording a short clip and sending it.
- Attach an image or file; the app encrypts it under MIP-04 and uploads it to a Blossom server.
- React to a message with an emoji to acknowledge it without typing a reply.
- Open the theme settings and switch between available themes to adjust the look while the app is running.
Pros & cons
- Group messages use MLS encryption with forward secrecy
- Open-source code under the MIT license that you can audit
- Free to use with no listed price
- Supports both Amber remote signing and local key login
- Voice messages, image sharing and reactions in one client
- Works on Windows, Linux, macOS and Android
- Interoperable with other Marmot Protocol implementations
- Requires understanding of Nostr keys and relays, which adds a learning curve
- Losing a private key can mean losing access to your identity
- Smaller user community than mainstream messaging apps
- Development is ongoing, so features and interfaces may change between releases
- Latest code update is recent but the project is not a large commercial product with formal support
Is OpenChat safe?
OpenChat handles private keys and encrypted messages, so take basic precautions. Download only from the official website or the GitHub Releases page, verify the SHA-256 checksum or signature when the project publishes one, and never enter your private key on a third-party website that claims to offer OpenChat. Using the Amber signer keeps your key out of the app entirely, which reduces exposure if the app itself is compromised.
Because MLS and NIP-44 protect message content, the main risks are operational rather than technical: lost keys, a compromised device, or sharing a key by mistake. Keep backups in a secure location and do not post them in chats. Check the releases page for the newest version, since the latest code update is dated October 2026.
- Official source only. Download from github.com/DavidGershony/openChat. Ignore ads and lookalike domains.
- Check the SHA-256. Compare the installer hash with the value the developer publishes before running it.
- Never share your seed phrase. No developer, support agent or website — including CryptApps — will ever ask for it.
Alternatives
Among the similar programs in this catalog, OpenChat focuses specifically on encrypted group messaging through the Marmot Protocol and MLS. Clients such as Amethyst and Gossip are general-purpose Nostr clients oriented toward public notes and feeds, where private group encryption is less central. Coop is closer to OpenChat in spirit because it concentrates on personal messages on Nostr, but OpenChat's MLS group layer is the distinguishing feature.
Tools like NAK and Nostr Commander RS are command-line utilities rather than graphical chat clients, so they suit scripting and testing rather than everyday conversation. Vega offers a cross-platform desktop experience for Nostr more broadly. If your priority is secure group chat rather than browsing a public feed, OpenChat is the more specialized choice.
Specifications
- Price
- Free
- Type
- Open source
- License
- MIT
- Latest version
- v0.7.9
- Last update
- 1 Oct 2026
- Windows support
- Yes (Windows build or installer)
- Source code
- github.com/DavidGershony/openChat
Frequently asked questions
Yes. OpenChat is listed as free and is released under the MIT license, which permits use, modification and redistribution. Because it is open source, you can review the code on GitHub before running it. Check the official releases page for the current version.
OpenChat uses MLS for group encryption and NIP-44 for direct messages, which protect message content from relays and other outsiders. Safety still depends on how you manage your keys and devices, so use the Amber signer where possible and download only from official sources.
The Marmot Protocol is a specification for end-to-end encrypted group messaging over Nostr, built on MLS. OpenChat is a client for it, and because the protocol is shared, other implementations can interoperate with the same group conversations.
You need a Nostr identity, which is a key pair rather than an account on a company server. You can sign in with the Amber signer or a local nsec key. Creating and securing that key is the first step before you can join or start conversations.
Amber uses NIP-46 remote signing, so the app asks a separate signer to sign events and your private key never enters OpenChat. A local nsec key is stored and used directly by the app, which is simpler but means the key is exposed to the device it runs on.
Yes. Voice messages are recorded and encoded with Opus, and images or files are encrypted under MIP-04 before being uploaded to a Blossom media server. The recipient receives the attachment in the conversation.
Yes. The project lists Windows, Linux and macOS for desktop, plus Android, and also mentions Docker among its platforms. The Windows build is the one covered on this page.
Verdict
OpenChat is a good fit for people who want encrypted group chat on the Nostr network and are comfortable managing a cryptographic identity. Its MLS-based group encryption, forward secrecy and open MIT-licensed code set it apart from general Nostr feed clients. Users who need a simple, centralized messenger with account recovery should look elsewhere, while those who value privacy and auditability will find it a thoughtful choice.