There are a lot of tools for fly ID, but few that can be used by non-experts in the field. @aispinsects , @upupa-epops , and I have collected diagnoses, with global family coverage but focusing on North America for genera and species, at https://sites.google.com/view/flyguide/diptera .
I’m posting this here because I’ve been told that interested people may not find this elsewhere. I hope this helps!