Minicom. I've got it running permantly on TTY5 configured to COM1 so I can control my "other" linux box when I need kernel debug output or I've mangled it's NIC/runlevel/whatever so bad that I can't SSH.
If you're using a shell over NULL modem cable from Amiga to Linux, don't forget to set the TERM environment variable.
export TERM=ansi _or_ if that doesn't work as expected perhaps:
export TERM=vt100. Depends what your miggy's term emulation is set to.
Of course, there's still zmodem etc. file transfer 'n stuff you would expect from normal term. programs.
- Paul