Delta Chat looks and feels like other popular messenger apps, but does not involve centralized tracking and control. The app 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 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. You can export all your chat data on one device, import it on a new device and happily continue chatting. Not requiring mobile numbers avoids cell-tower and other tracking.
Delta Chat establishes end-to-end encryption automatically when chat partners start communicating with each other. On a two-people chat, just send a "Hi!" message and already receive an encrypted reply if the other side accepts you as contact. End-to-End encryption not only works between Delta Chat apps, but also with other e-mail apps if they support the Autocrypt Level 1 encryption standard.
Moreover, Delta Chat offers an experimental "verified group" chat guaranteeing end-to-end encryption to be secure against active network or provider attacks. This unique feature is based on recent usability and cryptographic research and is going to be refined after further user-testing with at-risk users in 2019.
Delta Chat offers instant chatting and synchronization across devices. Messages sent on one device will quickly show up on other devices. There is an early iPhone version and mostly stable downloads for Linux, Mac OS Laptops and an experimental Windows download. All Desktop versions can be used standalone or in conjunction with a mobile version.
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, setting up new experimental mail servers ... or a donation if you can.
We currently use monetary donations to help contributors join us at our repeated one-week long gatherings -- where we develop and user-test with locals and evolve new directions and plans.