So #Nostr itself is a protocol and there are many clients (Native Apps, PWA’s, Desktop, Browser) like nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955 & nostr:npub142gywvjkq0dv6nupggyn2euhx4nduwc7yz5f24ah9rpmunr2s39se3xrj0 for mobile devices which allow you to interact with the protocol in a decentralized social media way, but there are TONS of other use cases for #Nostr and many diff clients which are not social medias, check out https://nostrapp.link or https://www.nostrapps.com