Reminder that the X11 based x3270 client can be used to communicate with mainframes, including the "Hercules" IBM mainframe emulator that you can run on Linux/Windows/MacOS .
x3270 for X11 based (it has buttons to click to send PF keys etc.)
c3270 for curses-based (terminal)
tcl3270 for using TCL to script interactions with a 3270 session
s3270 for some other form of scripting 3270 sessions