Links
Free Software
When you're setting up a computer system for a user there's one thing they always appreciate: free* software. These applications provide a cheap, legal alternative to costly monsters like Microsoft Office and Photoshop.
Wordprocessing, spreadsheets & slideshows
A highly-featured alternative to Microsoft Office that can read and write
most MS Office files.
Available for Windows, Linux, OS X and FreeBSD operating systems.
Web Browsers
I've been using Mozilla-based browsers for 10 years so I'm obviously a bit biased when it comes to Firefox.
This excellent browser is available for Windows, Mac OS X and Linux platforms and comes in a wide range of languages.
Internet Explorer may be the most widely used browser on the planet but
that's got more to do with its inclusion in Windows (and on ISP disks) and
less to do with its poor interpretation of web standards.
It's available for Windows, Mac OS 8 & OS X, and Windows Mobile (PocketPC).
Version 7 may feature some dramatic functional improvements but the user interface leaves a lot to be desired.
Opera is a very fast browser that pioneered tabbed browsing and page zoom.
It's available for a very wide range of platforms, including Windows,
Mac OS X, Linux, FreeBSD & Solaris, Windows Mobile (PocketPC)
and a range of mobile phones.
Don't forget Linux! Konqueror is a very popular web browser and file
manager. It was designed for the KDE desktop shell but can also be used with Gnome.
Graphics — Basic
Tux Paint is an award-winning drawing program for children ages 3 to 12.
It has an easy-to-use interface, fun sound effects, a friendly penguin
and runs on Linux and Windows.
Graphics — Advanced
The GIMP is a powerful photo and graphics manipulation program
comparable to Adobe Photoshop but missing some of the industrial
colour-matching features.
Available for Windows, Linux and OS X.
Blender is a tool for producing 3D graphics and animation.
Although not quite as popular aa commercial products 3D Studio Max and Maya,
Blender has been used to create CGI and animatics on a number of major movies
including Spider-Man 2.
Available for Windows, Linux and even Windows Mobile (PocketPC).
PDF viewers
From the company that invented PostScript and PDF files, this program can
run stand-alone and as a browser-plug-in and is available for a very wide
range of operating systems including Windows (3.1, 95 / 98 / Me,
NT4, 2000 / XP / 2003, Vista, CE / PocketPC / Mobile),
Linux / Unix / Solaris / AIX / HP-UX, Mac OS7-9 /
OS X, OS/2, Palm OS and Symbian. Phew.
* That's free-as-in-beer (i.e. gratis) rather than free-as-in-speech (i.e. liberty).