When you say "they to me" it makes it sound like you want a peer-to-peer connection. Unless your internet service allows unsolicited incoming connections, then you will need to do NAT piercing. And if you are behind the same NAT (e.g., same ISP) then you will have to forward traffic through some third host who is not behind the NAT.

But when you mention "wall(1)" it makes it sound like you want to connect to some internet accessible UNIX host via ssh and chat to others who are also connected to that host.

Option 2 would be less complex.

Depending on what software is installed on the host you connect to, there are many possibilities. Back in the old days, talk(1) could be used for split screen chats. Today, tmux(1) would be my choice. Anything that uses UNIX domain sockets could work.

Proof of concept:

Does Darwin have logger(1), syslogd(8) and /etc/syslog.conf(5)?

Decide where to log the messages, e.g., /var/log/messages

Edit /etc/syslog.conf

Start syslogd

logger "your message"

less /var/log/messages

less -F /var/log/messages

tail -f /var/log/messages

Messages have date, time, priority (if any) and hostname.

You said "something basic"; this is about as basic as it gets.