A key distinguishing factor is that iroh is meant to be used as a library that you can embed into your desktop, mobile or embedded apps.

Up to now our users are mostly teams that have a rust or C/C++ core, such as https://delta.chat/ . But now that we have bindings teams who use other languages should be able to use iroh.

So you can write e.g. an android and ios app that uses iroh direct connections under the hood, and the app user does not have to know or care about this at all.

We keep thinking about ways to combine iroh + zeroMQ! I think these two could compose. (Not familiar with nanomsg myself)

About tailscale: It's similar, but iroh is not a VPN, so it doesn't add a TUN interface. Instead, you'd build iroh directly into your application. Using iroh you can build a VPN, and there are projects that do so (iroh-lan/iroh-vpn are some hobbyist projects). The upside of building it into your application is that it doesn't need special permissions and is easy to ship to the user.