Prosody is an XMPP communication server designed to be easy to set up and light on system resources. XMPP is an open protocol for chat and messaging, so organisations, families or friends can run their own server, decide who they connect to and use a wide range of desktop and mobile client apps. Prosody can link up with other XMPP servers, and developers can extend it with modules.
Prosody is open-source software under the MIT licence. The project website names no company or foundation, and copyright in the source code is held by individual developers. The lead developer's public profile shows the United Kingdom and that of another core developer shows Sweden. You install Prosody on your own server, so messages and account data stay under your control; the website does not mention a hosted service from the project.