HECnet

The HECnet is a network of various DECNET machines across the internet. Using a specialized bridge program, people have bridged together their systems.

From the homepage:

What is HECnet? 

HECnet is a DECnet that connects different people who play around with different DEC machines. 
The network should not be regarded as a serious networking setup, nor should it be expected 
to work 24/7. It's a hobby project between people who think it's fun to create a DECnet network. 
HECnet is basically a DECnet phase IV network. Currently, the main router is a PDP-11 
running RSX-11M-PLUS. The machine is located in Uppsala, Sweden. 

The connectivity between nodes can be anything that works. The current connectivity is with 
an ethernet bridge between sites. Other solutions that have been used are a virtual serial 
async. connection talking DDCMP. Other possibilities are GRE and DECnet over IP.