The Nostr protocol supports many types of "messaging" applications... and the protocol is being extended continuously to support more.

Different clients can specialise on one type of activity... Or be super clients that do a lot.

Examples of what functionality can be done over Nostr

Twitter

Instagram

Wikipedia

Reddit

Spotify

WhatsApp

Ebay/Craigslist

GitHub

Blogs

Vlogs

Podcasts

Games

#amethyst is an android "super client" that does many of the above