In the beginning, the Internet was flat.
Every computer had a "real" IP address. If you wanted to send me a file, you could just connect to my computer and upload it.
A flat open network made things easy, but it also presented a security challenge. If we think we have security problems today, they are nothing compared to the widespread vulnerabilities and almost total lack of encryption that prevailed in the early days.
As the Internet opened up, firewalls were put into place to limit access to otherwise insecure devices. IPv4 address space limitations also played a significant role, requiring the deployment of NAT (network address translation) to allow an increasing number of devices to connect.
Security has improved since the early 1990s. Back then systems were routinely vulerable to remote attacks that let attackers enter and often take full control of the machine from anywhere on the network. Today attacks of this severity are much more rare, and most security threats are more sophisticated. Firewalls are still standard practice, but the risk of going without one is substantially less for a well-configured and up to date system.
The beneifts of a flat open network are many. It makes easy things like transferring files and data easy, and lets developers experiment with novel network protocols and technologies without having to worry about the complexities of implementing NAT traversal and device location.
Segmented networks are also a reason so many special-purpose "silo" cloud services exist as middle-men for our data, exposing us to widespread surveillance and security risks in the process. Without so many barriers in the way, we could just... connect.
ZeroTier was founded to directly connect the world's devices. We think flat, open networks are the future. It will take some time for security and authentication to get good enough to make open networking mainstream again, but in the meantime we wanted a way for users and developers to experiment.
So we created the public network. A public network is just a ZeroTier virtual network with no access control. Anything can join. To create one, just un-check the 'private' box on our network adminsitration interface (or run your own controller).
If you want to try out an open network, you don't need to create one. Just join 8056c2e21c000001. It's a network called Earth.
You'll receive an IP address in the 184.108.40.206/7 range (220.127.116.11 to 18.104.22.168), an "unrouted" IP range not used on the normal Internet. Every other member of Earth also has an IP in this range, so any two members of Earth can freely connect.
Once you're online, visit http://earth.zerotier.net/ for a test page, or ping earth.zerotier.net just to check connectivity.
You can also try pinging 22.214.171.124, though it won't always be online. That's my laptop.
Earth currently has no registry of services, but multicast-based service announcement protocols like mDNS/Bonjour will work. Sometimes you can see things like iTunes shared music or people available for Bonjour chat.
Security is your responsibility. Please take care to turn off unwanted services on your system prior to joining. If you do run services make sure they are properly protected by passwords or some other form of authentication. We are not responsible for any security problems.