It is a docker image (supervisor) they manage HomeAssistant docker and give a interface to control itself over UI. It have a own eco system with addons to extend the functionality in a easy way.

HassIO-Addons | HassIO-Build

HassIO is at the moment on development and not ready to use productive!

Feature in progress

Backup/Restore
DHCP-Server addon

HomeAssistant

SSL

All addons they can create SSL certs do that in same schema. So you can put follow lines to your configuration.yaml.

http:
  ssl_certificate: /ssl/fullchain.pem
  ssl_key: /ssl/privkey.pem

Install on a own System

Generic Linux installation: https://github.com/home-assistant/hassio-build/tree/master/install
Hardware Images: https://github.com/home-assistant/hassio-build/blob/master/meta-hassio/