Lightning: not really for you, it's for Salesforce stuff.
Atlaskit: not really for you, it's for Atlassian stuff.
Polaris: not really for you, it's for Shoptify stuff.
Photon: not really for you, it's for Firefox stuff.
Material Design: it's kinda for you, but it makes you look like you're Google-branded.
Bootstrap: definitely for you.
But I do with they were more clear about who they are for.