• Eternity Service by Adam Back is an overlay network on the Usenet.
  

• Dat/Beaker is closely integrated with the WWW and version 1.0 of it uses the Hypercore Protocol.
• Dissent is an academic project that aims to implement a fancy mixnet based anonymization network.
  
• Freenet is closely integrated with the WWW.
• I2P is closely integrated with the WWW.
• Publius is closely integrated with the WWW and it is a lot like the ZeroNet, except easier to censor and a typical abandoned academic project.
• Tor is closely integrated with the WWW.
• ZeroNet is closely integrated with the WWW.
• The WWW

• FidoNet is telephone network based.
• Gopher
• Usenet  is telephone network based.

• https://en.wikipedia.org/wiki/Videotex was an American system
  
• https://en.wikipedia.org/wiki/Minitel was the French system
  

Other Early Linked Document Systems

• Apple HyperCard was a proprietary system that was never properly marketed.
  

• The Ted Nelson certainly deserves an honorable mention.

• Fluence
• LBRY

• https://en.wikipedia.org/wiki/Category:Pre%E2%80%93World_Wide_Web_online_services