http://lainyubrp2aabmxhepbttfdbl53dct2inqifs42buvpf6w44uiitbeqd.onion/blog/matrix.html
And end-to-end encryption, of course, but I'll look into it later. Implementations... It's bad. It's really-really bad. Most stable and maintained implementation of server-side, matrix-synapse is literally written in python! It's very heavy, resource intensive and slow monster .