Delta Chat

Delta Chat is a messenger that uses the largest, most diverse and decentralized communication system ever created: the existing e-mail server network. Just use your standard e-mail account and start chatting with any of your e-mail contacts, whether they have installed Delta Chat or not.
Technically, Delta Chat is an e-mail application but with a modern chat interface. E-Mail in a new dress if you will. Chat and contact data remain on your devices. No uploads or centralized control of addressbook, calendar or other personal data. There simply are no Delta Chat servers where anything could be uploaded to.
Use Delta Chat with anyone out of billions of people: just use their e-mail address. Recipients will see a simple e-mail and may directly reply with their own e-mail app. They don't need to install Delta Chat, visit websites or sign up anywhere. If you send a picture or other media to a chat group your chat recipients will see a nice regular e-mail with an attachment. If they send a message and attachments back, you will see the media in your chat for this contact.
Delta Chat sends e-mails using your e-mail account and provider of choice. You can change mobile numbers without any trouble or even work without any SIM card or phone number at all. End-to-end encryption is established automatically when chat partners start communicating with each other.
Delta Chat is a relatively young project, but already has a lot to offer. It employs a pragmatic and usability-driven approach to decentralized messaging. No re-inventing of wheels unless one of them causes actual trouble or concern. We rather often think about removing technology than adding yet more of it, trying to keep things maintainable and understandable for us and others. Most popular programming languages and many human languages are involved in the development of Delta Chat apps and the various activities around it.
We are grateful for any help, be it contributing good bug reports, helping other users on the forum, participating in our open development with PRs and reviews, translations to more languages, working on new bots or setting up new experimental mail servers.