Be careful of rocketchat : beside some exotic technology choices (meteor), they seem to be in a dynamic of re-closing previously opensource parts of it. Something like that already occured with their ldap implementation (it needed some love, but sadly they give them closed-source love…)

you might want to add borg, restic and - more recently - plakar to that list

Why not something like NAS4Free or OpenMediaVault, then? You don’t have to chose between DIY and paid-for, there is a middle-ground

this. that’s why a model is as good as its known margin of error and limits

and it’s important to remember models work well outside of edge cases ; in your speedometer example, if you brake on ice and your car drifts out of control, the speedometer will show no speed, when you’ll probably have one … but in most cases, it’s a good enough model