I use different things:

• Netplan for the actual hard “inventory” like documentation. What cable goes where, what powers what, what MAC is assigned to what, when did I buy this or that?(The later with an addon). In theory I also have snipe-it,but doing it all in netplan is more convenient.

• Wiki.js for the concept and How-To-Side. Lots of draw.io diagrams (which can be done directly in articles), HOWTOs as a reminder for me, naming conventions, etc. Also some basic inventory information for disaster recovery. (Wiki.js is not hosted locally)

• Vaultwarden for all secrets,passwords, recovery keys, ssh keys,etc.

• And last but not least I do backups to Mdisc Blue Rays every few months. These include the documentation, the most important files (knx project for example), etc. and are stored at a different location (bank safe). There is also an detailled explanation in both my wifes and my own will how to access these so if something happens the kiddos or someone taking care of them can gain access.