I just installed atuin to try it out as I do my work this week, and when brew install atuin finished, it came with a note I had not seen before:

To start atuin now and restart at login:
  brew services start atuin

My immediate reaction was What the heck is brew services? It’s pretty much exactly what I expected:

Manage background services with macOS’ launchctl(1) daemon manager or Linux’s systemctl(1) service manager.

These seem to be scoped to homebrew.mxcl, so any activated services will be . Notably, brew services clearly also has some layer sitting on top of launchctl (and presumably systemctl on Linux): brew services list will show services that are not listed by launchctl list.