Tailscale uses MagicDNS which allows one to auto-generate a semi-memorable private hostname as well. I'm in the networking industry so I'm not seeing anything truly groundbreaking or that isn't offered elsewhere.
That being said, I think our use of QUIC multipath is pretty novel. If you use tailscale or a VPN, your connection (TCP or QUIC or whatever) won't immediately notice when the underlying transport changes (e.g. relay to direct or vice versa). So there will be some delays as the congestion controller learns about the underlying transport.
With the latest iroh using QUIC multipath, each path gets its own congestion controller, so switches of the underlying transport are more smooth.
Also, multipath allows us to treat custom transports as just additional paths.
IIUC you just send someone 'here is the connection information' and it just works automatically.
I love MagicDNS - A long time ago I wrote a stupid Python script to have it continually generate MagicDNS names until one of them contained a word I was looking for.