There are two different versions of talk in common use today. The first, dubbed "old talk," is supported by a set of Unix systems (most notably, those currently sold by Sun). The second, ntalk (aka "new talk"), is more of the standard. If, when attempting to talk with another user, it responds with an error about protocol families, odds are the incompatibilities between versions of talk is the culprit. It's up to the system administrators of sites which use the old talk to install ntalk for their users.
Wide Area Information Servers (WAIS)
The WHOIS Database
The main WHOIS database is run at the Network Information Center (NIC). The whois command will let you search a database of every registered domain (e.g. mit.edu) and of registered users. It's primarily used by system postmasters or listowners to find the Points of Contact for a site, to let them know of a problem or contact them for one reason or another. You can also find out their postal address. For example:
% whois mit.edu
Massachusetts Institute of Technology (MIT) MIT.EDU 18.72.2.1
Massachusetts Institute of Technology (MIT-DOM) MIT.EDU
Note that there are two entries for mit.edu; we'll go for the second.
% whois mit-dom
Massachusetts Institute of Technology (MIT-DOM)
Cambridge, MA 02139
Domain Name: MIT.EDU
Administrative Contact, Technical Contact, Zone Contact: Schiller, Jeffrey I. (JIS) JIS@MIT.EDU (617) 253-8400
Record last updated on 22-Jun-88.