Business that facilitate the creation and operation of protocols and software to allow individuals and businesses to do things peer-to-peer with only the Bitcoin blockchain as the final arbiter.

Bisq is an OG example of this.

Lightning was a huge step forward.

Nostr as a base layer for distributed application state via notes and relays took this further.

It would be nice to see bitcoin developing its own peer-to-peer complex transaction models that might be facilitated by a third party arbiter or oracle, instead of enmeshing itself more deeply with a flawed "tradfi" system.