Basic Unix commands:
ls, tr, sed, awk and so on (you name it, Linux probably has it).
Development tools:
gcc, gdb, make, bison, flex, perl, rcs, cvs, prof.
Languages and Environments:
C, C++, Objective C, Java, Modula-3, Modula-2, Oberon, Ada95,
Pascal, Fortran, ML, scheme, Tcl/tk, Perl, Python, Common Lisp,
and many others.
Graphical environments:
X11R5 (XFree86 2.x), X11R6 (XFree86 3.x), MGR.
Editors:
GNU Emacs, XEmacs, MicroEmacs, jove, ez, epoch, elvis (GNU vi),
vim, vile, joe, pico, jed, and others.
Shells:
bash (POSIX sh-compatible), zsh (includes ksh compatiblity
mode), pdksh, tcsh, csh, rc, es, ash (mostly sh-compatible shell
used as /bin/sh by BSD), and many more.
Telecommunication:
Taylor (BNU-compatible) UUCP, SLIP, CSLIP, PPP, kermit, szrz,
minicom, pcomm, xcomm, term (runs multiple shells, redirects
network activity, and allows remote X, all over one modem line),
Seyon (popular X-windows communications program), and several
fax and voice-mail (using ZyXEL and other modems) packages are
available. Of course, remote serial logins are supported.
News and mail:
C-news, innd, trn, nn, tin, smail, elm, mh, pine, etc.
Textprocessing:
TeX, groff, doc, ez, LyX, Lout, Linuxdoc-SGML, and others.
Games:
Nethack, several Muds and X games, and lots of others. One of
those games is looking through all the games available at tsx-11
and sunsite.
Suites:
AUIS, the Andrew User Interface System. ez is part of this
suite.
All of these programs (and this isn't even a hundredth of what is
available) are freely available.
Commercial software is becoming
widely available (Star Office).