Computer monitors display tones differently out of the box and as they age; Apple monitors display them differently from PC monitors. To be sure that your monitor is accurately displaying the greatest range of tones, you need to consult tools that help you calibrate your monitor.
Arachnophilia is not Open Source Software -- it's "Careware," but that's good enough for me. Originally popular as an HTML editor for Windows, Arachnophilia has been rewritten in Java for multiple platforms, and is now one of the most capable and configurable applications for editing HTML and supporting websites.
Dosemu lets you to run many DOS applications in Unix/Linux. It's not very easy to install and use, and there is little ongoing effort to improve it because fewer people are relying on DOS applications. Nevertheless, it can be very helpful for those still using excellent old DOS programs like WordPerfect 5.1 -- either for new work or for maintaining access to old work.
A capable cross-platform FTP client.
Photoshop is undeniably the most capable graphics editing application right now, but The GIMP is a close second, and both exceed most user's needs. If you use ten percent of what Photoshop offers, you'll use fifteen percent of what The GIMP offers. The GIMP has scripting tools that beat Photoshop, and an interface that many find more efficient than Photoshop's.
IceWM is a light-on-memory Unix/Linux window manager that makes a priority of supporting efficient keyboard commands to accomplish what most GUIs leave to the mouse.
Mozilla combines a browser, an HTML editor, and an e-mail client. Mozilla is still being developed, but emphasis has shifted to a stand-alone browser (Firefox) and a stand-alone e-mail client (Thunderbird), in addition to a calendar, an HTML editor, and other applications.
Openoffice.org is an alternative "office suite" mimicking Microsoft Office that runs in Unix/Linux, Windows, and Apple environments.
Tex is an almost perfect application for laying out manuscripts. Its author, Donald Knuth, pays a bounty to anyone who finds a bug -- but nobody has collected for years. Latex is a set of macros for dealing with Tex; Lyx is a "what-you-see-is-what-you-mean" application that eases the use of both. Writers and publishers preparing manuscripts for traditional publication -- especially those who use scientific and/or mathematical notation -- consider these tools unsurpassed.
http://www.troubling.info/comp.html