I'd like to point out that many law enforcement agencies run web-based embedded systems anyway, so the underlying system could EASILY be BSD, Linux or whatever. Currently, at least where I'm from, they use Windows XP Embedded, but having seen the backend I'd reckon they could swap it out and the only thing they'd notice was the switch from MS Office to LibreOffice. Maybe they'd notice a lack of ransomware attacks too, but you never know.

Paid software isn't free either. And if you think moving from Windows XP to 7 to 8 to 10 comes at less of a training cost, as moving to a *nix based system, you're simply wrong. The real caveat is that *nix admins are not cheap, they're not widely available and they often don't fit into the stereotypical view of an IT Supporter/Admin/Manager. Also, there's a real software hurdle, but as with everything, someone has to go first. If not, the monopoly never changes and we're all stuck with less secure, less serviceable and less innovative software. How governments are allowed to use closed software for critical systems and establishing a decade long dependency on 1 company, is beyond me. Bribery or incredible stupidity must be involved.

If you're looking for ease-of-use and Out-of-the-box experiences, ElementaryOS is working with that exact goal in mind. https://elementary.io/ It's still in beta, but I've used it for a few years, though recently switched to Arch, but have been using Debian, Mint, etc for many years before that. ElementaryOS is the linux distro you can easily give your mother and not worry about her breaking it, while still retaining all power-user options.