Like a marriage made on heaven Unix belongs to the network and the network to Unix. No matter witch flavor of Unix/Linux are you using certainly your OS was designed to connect and interact with other computers.
If you are in a Linux distribution you can do
ls /etc/init.d and se with your own eyes all the service you OS can provide. In fact lot of them probably are already running. You computer can provide services of many kind each one of those are executed and managed by one of those programs that runs in background by the system user and are call deamons.
On the other side can also find lot's of clients for those services and more. A perfect match. Client and Servers all together.
ftp File transfer program
rcp Remote file copy
rlogin Remote login to a UNIX host
rsh Remote shell
tftp Trivial file transfer program
telnet Make terminal connection to another host
ssh Secure shell terminal or command connection
scp Secure shell remote file copy
sftp secure shell file transfer program
git Git client
nslookup Perform searchers on DNS servers
rsync Rsync client that let you sync up directories using ftp or ssh protocols
But sometime you just need simple programs to administrate your network
ping
netstat Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
finger
ifconfig
wget
Because networking it's essentially communication each other on your system you could found small console programs to send information and chat. This is literally the beginning of moderns mail and chat services. This is the old way universities communicate with each other.
mail Simple send or read mail program
mesg Permit or deny messages
talk Talk to another user
write Write message to another user