I have discovered delta chat for several years already (I help in the testing phase and participate quite actively on the forum) and I find it great, in the last year/year and a half I have replaced whatsapp with delta chat to communicate with relatives and close friends (at least the ones I managed to convince to use it). Also delta chat in addition to normal chat features has interesting aspects like bots and webxdc. It is not without flaws but if you use it with a suitable email provider it is truly remarkable.