Best open-source alternatives to Twilio

Novu is an open-source communication infrastructure platform built for products and agents that need to talk to users across multiple channels. It provides a single API and unified conversation model so teams can avoid wiring up separate notification systems, webhook handlers, and provider integrations for each channel. The project is aimed at developers building inboxes, notification centers, workflows, and agent messaging experiences. It supports channel delivery across inbox/in-app, email, SMS, push, chat, Slack, Microsoft Teams, Telegram, WhatsApp, and more, and it includes embeddable UI components plus SDKs so teams can integrate the system into existing applications or agent stacks.

ntfy is a simple HTTP-based publish/subscribe notification service that lets users send push notifications to phones or desktops from scripts and other automation. It is aimed at people who want lightweight notifications without having to sign up or pay, while also allowing self-hosting for those who want to run their own instance. The project includes a hosted public service at ntfy.sh, documentation for publishing and installing, and companion mobile apps for Android and iOS. It also offers paid hosted plans for users who prefer not to self-host, but the core software is open source and designed around straightforward HTTP PUT/POST message delivery.

Janus is an open source, general-purpose WebRTC server developed by Meetecho. It is aimed at developers and teams building real-time communication systems that need a media gateway rather than a client application. The project is presented as the newer multistream branch of Janus, with the repository intended primarily for Linux systems and also buildable on macOS. The README emphasizes a modular, dependency-driven architecture: core functionality can be extended with optional components for REST, WebSockets, data channels, SIP, messaging backends, and media-related plugins. Installation is done by compiling from source after satisfying library dependencies, with package commands shown for Fedora and Debian/Ubuntu, and additional guidance for manually building libraries such as libnice, libsrtp, BoringSSL, usrsctp, and libwebsockets.

Fonoster is a programmable telecommunications platform positioned as an open-source alternative to Twilio. It is aimed at businesses and developers that need to build voice-driven applications, automate call flows, and expose telephony capabilities through an API-first stack. The README shows that the project supports multitenant deployments, role-based access control, OAuth2 and JWT authentication, and integrations such as S3 and Google Speech APIs. Developers can build voice applications using the provided SDKs and voice verbs, then deploy them as services that handle call control, speech, DTMF gathering, recording, and call routing. The project also provides guidance for self-hosting with Docker and points users to its documentation for quickstart and deployment instructions.

FreeSWITCH is an open-source software-defined telecom platform designed to replace or complement proprietary telecom switches. It is aimed at developers, telecom operators, and organizations building voice, messaging, and programmable communication systems on commodity hardware ranging from Raspberry Pi devices to multi-core servers. The project can be obtained from source on GitHub and built for multiple operating systems including Linux, Windows, macOS, and BSD. The README highlights package-based installation guides, source build instructions, downloadable tarballs and Windows installers, and documentation hosted on the FreeSWITCH Confluence site. It also emphasizes integration with SignalWire, which provides hosted cloud services and extensions such as SMS, SIP, serverless application hosting, and programmable telecom capabilities.

Kamailio is an open source SIP signaling server intended for building and operating real-time communications services. It is aimed at telecom operators, carriers, enterprises, and individuals that need VoIP, instant messaging, and presence functionality on top of the SIP standard. The project emphasizes scalability, robustness, security, and flexibility, and it is positioned for large deployments with substantial call volume and subscriber counts. It is developed by a worldwide community, with documentation, tutorials, module references, and installation guidance published on the project website and wiki. The README also points users to source-based installation instructions and Linux package repositories for Debian and RPM-based systems.

OpenSIPS is a SIP server project aimed at VoIP and signaling infrastructure use cases. The README describes it as a GPL-licensed implementation that originated as a fork of the SER project and emphasizes a more open development model with external contributions and faster feature delivery. The project is maintained by OpenSIPS Solutions and is organized around modules, with module-specific README files and a published online documentation site. The README also points users to tutorials, examples, and public mailing lists for usage, development, business, and project news, indicating that it is intended for both operators and contributors working with SIP-based telephony systems.

Notifo is a notification platform designed for collaboration tools, commerce sites, media products, and other applications that need to deliver messages to their users. It provides a central service for creating notification events, matching them to user subscriptions, and delivering them through multiple channels such as web sockets, web push, email, mobile push, and SMS. The project includes both a backend service and a management UI. It supports topic-based subscriptions, configurable notification preferences, confirmation states, and delayed sending to reduce unnecessary alerts. The README also shows that it is intended for self-hosting, can be run with Docker or Docker Compose, and is built on an ASP.NET Core and React stack with MongoDB as the current database backend.

PushBits is a self-hosted relay server for push notifications. It is aimed at users or teams that want to send alerts through a straightforward web API while receiving them in Matrix rather than via a dedicated push app. The project positions itself as a Matrix-based alternative to services like Pushover and Gotify, with a focus on reusing an established messaging platform for delivery. The server supports multiple users and multiple channels per user, and it includes tooling for both API-driven and CLI-based administration of users and applications. It also advertises compatibility with Gotify’s sending API, optional checks for weak passwords using Have I Been Pwned, and Argon2-based password storage. The README indicates the project is still in alpha, and the documentation and API docs are hosted online.

Flexisip is a C++17 SIP server suite designed to provide the backend for VoIP and messaging services. It combines several server roles in one modular system, including SIP proxying, presence, conferencing, push notifications, registration events, and B2BUA functionality for identity translation, transcoding, and SIP trunking. The project is aimed at operators and developers building server-based telephony services as well as embedded communications deployments. The README describes deployment on server machines for a full VoIP service and also notes that it can run on smaller hardware, with configuration generated from a default config file and the project built from source, packaged as RPM/DEB, or built into a Docker image.