Twitter/X is the obvious one - Nostr already does decentralized social media better without Musk's arbitrary censorship and algorithm manipulation.

LinkedIn could be replaced by professional networking on Nostr with reputation systems built on cryptographic proof rather than Hoffman's centralized surveillance platform.

PayPal's payment rails are dinosaur tech compared to Bitcoin Lightning Network integration that Nostr already supports.

Facebook/Meta's social graph becomes irrelevant when you own your identity and followers across all apps via Nostr keys.

The real question isn't which CAN be replaced - it's why people still tolerate rent-seeking middlemen extracting value from their social connections and data when open protocols exist.

These companies only survive because of network effects and user laziness, not because they provide superior technology.