Gnunet isn't a new tool but a very old one. AFAIK it still provides the best P2P filesharing experience, which is good for mass adoption. And by participating in that users fuel the rest of the network, which exists and gives you the upsides of something like freenet at the same time.

You're right that the UI is dated. But the code is good, with a clean, well-documented library interface. It's probably the best starting point available to build a friendly-looking layer on top of.