I once did this for shits and giggles on a secondary box and have decided (partially inspired by the
Warez Free thread] to detail the process.
I started with a fresh install of Windows 2000 and decided to replace as many of the Microsoft components and utilities as I could with freeware alternatives, preferably but not exclusively ones under the GPL.
I started with the very heart and soul of Windows, the Explorer front end. I replaced this with
Litestep. I was pleasantly surprised to find that in addition to providing nearly limitless customization and myriad skins, Litestep actually used less system resources than Explorer, meaning the end result was faster too. I couldn't very well replace the front end and still use the Explorer file manager, so I swapped that out for
ExplorerXP, a freeware alternative that adds such brilliantly obvious features as tabs and batch renaming.
With the two easily replacable key elements replaced, I moved onto applications.
Winamp 5 was the obvious choice as a media player, as was
Firefox for browsing and
Thunderbird for email. Less obvious but equally useful, I replaced notepad with a
Windows implementation of VIM and added
Irfanview for image viewing and
The GIMP for image manipulation. I rounded all of this off with
Open Office.org for document editing. The end result - over the course of a day I used no part of the regular Windows front end on that box. The back end was obviously all still Windows, but there's only so much you can do.
If I ever try this again, I may look at ways to take it a step further, perhaps with an alternate TCP/IP stack (although according to the rumours, the Win2k TCP/IP stack is actually lifted from BSD anyway) or some of the other easily replacable back end components. Anyone have any suggestions on this?