Carey Evans maintains x3270 for Debian. He has a page that documents how to use x3270 to access AS/400 hosts.
Valerio Di Giampietro maintains an AS/400 and Linux page which uses s3270.
Don Russell developed the x3270 extensions for the RPQNAMES Query Reply. His webpage includes additional documentation and tools for this facility.
py3270, a Python interface to s3270 and x3270.