http://dwebkjkovsjobzrb45dz6prnlifnapiyp2dba33vcmcsaikr2re4d5qd.onion/knowledge/what-is-hidden-service
Some examples of these include FTP (File Transfer Protocol), SSH (Secure Shell), Telnet, SMTP (Simple Mail Transfer Protocol), and the Jabber/XMPP messaging service. Each of these services is hosted through the Tor anonymity network, adding an extra layer of security and privacy.