Matrix: https://github.com/matrix-org/matrix-spec/tree/main/data/event-schemas/examples

ATproto: https://atproto.com/specs/atp

Fediverse:

- ActivityPub https://www.w3.org/TR/activitypub/

- ActivityStream 2.0 https://www.w3.org/TR/activitypub/

- Mastodon's "things" https://docs.joinmastodon.org/spec/activitypub/

Meanwhile, Nostr:

struct {

char* id;

char pubkey[64]; // fixed

char* sig;

char* content;

uint8_t kind;

uint8_t created_at; // forgot if unix timestamp is 8 or 16...

char** tags;

}

enum {

PROFILE = 0;

// ...

}

Done.