First of all: consider using a reasonable OS. There is a whole zoo of nice, nifty, mighty alternatives to Redmond's toaster firmware, they are fast, stable, network capable, secure - and many of them don't cost a buck. Did I mention that you can have a look at the sources and find out if there's someone spying on you?
Want to learn how your machine works? Have a look at MINIX, a simple Unix-like (and POSIX - compliant) OS implemented using a microkernel).
Linux), monolithic. If you need one, have a look here.
FreeBSD - secure and stable.
NetBSD - runs on almost every piece of hardware.
OpenBSD - the most secure of the three.
Tor (The Onion Router) helps to protect your privacy via a distributed network of anonymous nodes.
dansguardian: this is a real contentfilter (as opposed to a content blocker). This nifty piece of software combined with a reasonable proxy filters webpages based on content, not origin. Add ip rules to create a transparent proxy and china will probably be safe until the kids learn how to boot your main proxy from floppy/CD/USB/[add option here].
Ever banged your head into a keyboard while trying to create a simple bargraph of some statistical data? If so, gri, a language for scientific graphics programming might be your tool. The site states that, like latex, gri 'provide[s] extensive power in exchange for patience in learning syntax.' - very nice!
Scigraphica, quite close to Origin.
Scilab - an open source package for numerical computation that can do very nice graphics.
ImageJ, written by W. S. Rasband at the U.S. National Institutes of Health, Bethesda, Maryland, USA: this thing has only one disatvantage - it's java, literally stopping my machine.
Quite often the gimp (Gnu Image Manipulation Program) comes handy.
Fityk, a program for nonlinear fitting of analytical functions (especially peak-shaped) to data. Very nice for fitting peaks to XRD measurements or analyzing spectroscopic data.
again, Gnuplot - a classic.
mathomatic is a highly portable, general purpose Computer Algebra System, which can solve, simplify, and compare algebraic equations, perform calculus transformations and generate efficient C or Java code from equations.
Universal: TeX/LaTeX, on a real OS people tend to use teTeX. This is the text processing system (Word? That's something a human being articulates to communicate, right?).
What to do if somebody sends a MS-Word-'document' (and, for some reason, you are not able to beat the person with his own leg)?
If you like colorful graphics and lots of little buttons: openoffice or libreoffice, capable of reading many MS-Office formats.
Antiword converts binary MS-Word-Files (2, 6, 7, 97, 2000, 2002 and 2003) to Plaintext or Postscript on many (really!) older platforms.
"Despite the fact that open formats like RTF are good and widely avialable, far too many idiots seem to insist on using Word .doc format. This program is an attempt to limit the damage this causes users of non-Microsoft systems and text processing systems, for example LaTeX."
Trying to layout posters, flyers or similar? Have a look at scribus for professional page layout in many different operating systems.