Fonoster: The open-source alternative to Twilio
Fonoster is researching an innovative Programmable Telecommunications Stack that will allow businesses to connect telephony services with the Internet entirely through a cloud-based utility.
Features
The most notable features of Fonoster are:
- Multitenancy
- Easy deployment of PBX functionalities
- Programmable Voice Applications
- NodeJS SDK
- Support for Amazon Simple Storage Service (S3)
- Secure API endpoints with Let's Encrypt
- Authentication with OAuth2
- Authentication with JWT
- Role-Based Access Control (RBAC)
- Plugins-based Command-line Tool
- Support for Google Speech APIs
Code Examples
A Voice Application is a server that controls a call's flow. A Voice Application can use any combination of the following verbs:
Answer- Accepts an incoming callHangup- Closes the callPlay: Takes a URL with a media file and streams the sound back to the calling partyPlayDtmf- Takes a DTMF sequence and plays it back to the calling partySay- Takes a text, synthesizes the text into audio, and streams back the resultGather- Waits for DTMF or speech events and returns back the resultSGather- Returns a stream for future DTMF and speech resultsStream- Creates a bidirectional stream to send and receive audio from a callerDial- Passes the call to an Agent or a Number at the PSTNRecord- It records the voice of the calling party and saves the audio on the Storage sub-systemMute- It tells the channel to stop sending media, effectively muting the channelUnmute- It tells the channel to allow media flow
Voice Application Example:
const VoiceServer = require("@fonoster/voice").default;
const {
GatherSource,
VoiceRequest,
VoiceResponse
} = require("@fonoster/voice");
new VoiceServer().listen(async (req: VoiceRequest, voice: VoiceResponse) => {
const { ingressNumber, sessionRef, appRef } = req;
await voice.answer();
await voice.say("Hi there! What's your name?");
const { speech: name } = await voice.gather({
source: GatherSource.SPEECH
});
await voice.say("Nice to meet you " + name + "!");
await voice.say("Please enter your 4 digit pin.");
const { digits } = await voice.gather({
maxDigits: 4,
finishOnKey: "#"
});
await voice.say("Your pin is " + digits);
await voice.hangup();
});
// Your app will live at tcp://127.0.0.1:50061
// and you can easily publish it to the Internet with:
// ngrok tcp 50061
Everything in Fonoster is an API first, and initiating a call is no exception. You can use the SDK to start a call with a few lines of code.
Example of originating a call with the SDK:
const SDK = require("@fonoster/sdk");
async function main(request) {
const apiKey = "your-api-key";
const apiSecret = "your-api-secret"
const accessKeyId = "WO00000000000000000000000000000000";
const client = new SDK.Client({ accessKeyId });
await client.loginWithApiKey(apiKey, apiSecret);
const calls = new SDK.Calls(client);
const response = await calls.createCall(request);
console.log(response); // successful response
}
const request = {
from: "+18287854037",
to: "+17853178070",
appRef: "3e61ecb7-a1b6-4a93-84c3-4f1979165bca",
// Optional metadata to be sent to the Voice Application
metadata: {
name: "John Doe",
message: "Please call me back."
}
};
main(request).catch(console.error);
Getting Started
To get started with Fonoster, use the following resources:
- Deploying Fonoster with Docker
- Guide for Early Access User
- Getting started with Fonoster
- How we created an open-source alternative to Twilio and why it matters
Give a Star! ⭐
Please give it a star if you like this project or plan to use it. Thanks 🙏
Bugs and Feedback
For bugs, questions, and discussions, please use the Github Issues
Contributing
For contributing, please see the following links:
Sponsors
We're glad to be supported by respected companies and individuals from several industries.
Find all our supporters here
Authors
License
Copyright (C) 2026 by Fonoster Inc. MIT License (see LICENSE for details).