Messenger Developers Official Homepage. Resources to build a messenger bot including plugins, SDK, features, tutorials, API, FAQs, updates, a community of developers. WhatsApp Messenger is a freeware, cross-platform messaging and Voice over IP (VoIP) service owned by Facebook. It allows the sending of text messages and voice calls. Yahoo Messenger will no longer be available after July 17, 2018. Find the answers to your questions and read how to download your conversations into a permanent.