zigbee2mqtt is a nice little piece of software that allows you to connect zigbee devices without the need of proprietary gateways. It’s based on zigbee-shpeherd and it runs on nodejs. You can read more on the forums or directly in the documentation
Hass.io Add-on: zigbee2mqtt is a packaged version of the above, focused on making it very easy to install and configure.
The addon is still having very short release cycles because of fast pace development of zigbee2mqtt but it’s stable enough for usage. Have a look at the extensive documentation and if you need extra support use the issue tracker.
How do Z2M releases get adopted by HA?
As I write, Z2M shows latest release 1.21.1 released on September the 1st whilst the latest available on my HA supervisor is 1.18.1 published on March the 2nd. The reason for me asking is that 1.18.1 has a bug I´m suffering from. This bug has been already fixed (https://github.com/nurikk/zigbee2mqtt-frontend/issues/821).