1. The co-ordination server for the initial handoff. You can self-host if you want
2. Derp relays (for actual traffic). you can also self-host (peer relays)
Actually if self-hosting is that important to you, there are also newer solutions like netbird and netmaker that might worth a look.
Yes, as I noted, those differences wouldn't stop you from sending data locally. But since parent originally requested how they're different (without stating what exactly is important for them), I figured it is important at least to note what actually is the difference between taildrop and Flipflop.
It'd seem then if you wanted "local-first P2P transfer", with taildrop you'd need ~3 separate services running, unless I misunderstand you? Flipflop seems to do all those things in one package, although again, signaling (for NAT punching) is still via a central server.
Tailscale is super popular with people that have a homelab or nas/cameras/photos etc, and they have already solved the NAT problem (which iroh itself markets).