MessageBird Voice API - Add programmatic call capabilities to your app or service
Dialogflow - Conversational UX Platform. (ex API.ai)
MessageBird Chat API - Connect with your customers through different messaging apps
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Voiceflow - Build voice apps in your browser without coding
Botkit - Botkit is an open source developer tool for building chat bots, apps and custom integrations for major messaging platforms.