There are now 4 fileformats:
.tar
.tar.Z
.archive (or .arc or with no extension)
.sfx     (self-extracting)
filename.filetype   (e.g. !help.text or !run.obey)

archivers/extractors for .tar/.tar.Z files:

compress       unixcomatible compress-program
tar            unixcompatible tar-program 
!tarZ          simple enviromentscripts for tar and compress

archivers/extractors for .archive files: (also called "spark"-files)

splug2.sfx     a archive-extractor, secompresses nearly everything
               (nearly all new uploads are Sparkplug 2.2X compatible)
arc            write/extractor for Arc-files
!warc          simple script to write spark-compatible files from a directory
               tree (you need arc, gawk and do)
unixcark       extractor under unix 
unixnspark     new extractor under unix
sparkinfo      look inside a sparkfile 
arcfs054       use (start copy) files from a archive