GNU Netcat seems to work to some degree (with -e) but can only support one user/session/instance, ideally I'd want to be able to connect more than once without having to restart the server.
socat can fork.
I suggest browsing it's examples
socat TCP4-LISTEN:5555,fork,tcpwrap=script \
a simple server that accepts connections (TCP4-LISTEN) and fork's a new child process for each connection; every child acts as single relay. The client must match the rules for daemon process name "script" in /etc/hosts.allow and /etc/hosts.deny, otherwise it is refused access (see "man 5 hosts_access"). For EXEC'uting the program, the child process chroot's to /home/sandbox, su's to user sandbox, and then starts the program /home/sandbox/bin/myscript. Socat and myscript communicate via a pseudo tty (pty); myscript's stderr is redirected to stdout, so its error messages are transferred via socat to the connected client.