Vim http://www.vim.org www.vim.org is an open source clone of vi, the de facto standard Unix text editor. Actually, it does lots of things that original vi doesn't; the name stands for vi improved. Or maybe vi improved.
Actually, the acronym VI stands for Vim Imitation. ;) Or Very Impossible.
See: Great Vim Features
Steve Oualline's Vim book is available under the Open Publication License (OPL):
On-line from the publisher (one jpeg file per page & an icky navigation interface):
www.newriders.com 
PDF for download:
www.truth.sk
Pure HTML version:
doesn't exist yet.
[Comments from Slick Edit page...]
Vim (www.vim.org ) has natively a rather cumbersome extension language, but you can compile it with an embedded Python interpreter, a Perl interpreter, etc.. Python definitely counts as a "modern O-O language".
I believe you can also use Ruby, if that's your sort of thing.
The 'native extension language' called (I think) Vim script works quite well, it's just a little ugly. You can use Python (or Perl) but for editing work there's usually no need - the editor itself has a myriad of builtin features that are very powerful.
The developer release of Vim 6.0 has the following of the features bulleted above:
Virtual Edit Mode
Column Cut and Paste
Fill Selected Area (including column(s) with Char)
Delete Selected Area (including column(s))
BadAss regular expression support
Hex editing thingy
And I've edited 200Meg files with it just fine.
Heck, I have edited MS Word files with it. ;-)
Is there some trick to this? Do you run them through antiword? Because Word files appear to not be text-based...
I'm using VIM 6.1, but it has a remarkably difficult time displaying (and colorizing) non-trivial XML files. (7/26/2002) I'm often forced to fall back to Notepad. (Ick!!!)
-- Jeff Grigg
Err, ah, you could just turn off the syntax awareness feature. I mean, really, notepad?? Extreme Masochism? -- Garry Hamilton
If you have xmllint installed, try formatting your XML markup with
:%!xmllint -format -
Aside from nicely indenting the XML, this will restore Vim's speedy syntax coloring (which apparently depends on line length). When working with large, unformatted XML files, I generally turn off auto-highlight for XML, then turn it on selectively.
You can turn off syntax highlight with :nohl
What about Vigor instead?
No. Vigor does not belong here, as it is based on nvi.
from VimTextEditors (probably can be deleted here):
Vi Improved. An excellent implementation of VI, the venerable Unix Os editor that originated at Cal Berkeley. It has lots of improvements and extensions over the original VI (hence the "Improved") and is available freely (Free As In Beer and free as in Open Source). If you don't want to build it yourself, there is almost certainly a binary available for your particular platform (nearly every Unix Os, Microsoft Windows, Mac Osx, etc.).
Mac Osx, at least, comes with Vim included, accessible from the command line. Just type "Vi" at the prompt in whatever shell you use.
See original on c2.com