CHUCK HOUPT  It's true that the top layer Cocoa UI is just a WebView,

but underneath that is a local copy of the W3C Validator (and supporting libs and modules), running inside a simulated CGI environment.

The setup is somewhat like a Dashboard Widget, in that the UI is mostly HTML, with scripts and libraries doing the work.

The goal of Validator S.A.C. is to "port" the W3C Validator as cleanly and simply as possible.

If you're interested in the details, take a look at the source, which is included with every copy (select Help > Show Source Code).  
(Version 0.5)

CHUCK HOUPT  The Less Termlet can be launched from the command line with the open command:

% open -a Less apache_log

This will open a new Terminal window for less, which is close to what you describe. Wrapping 'open -a Less' in a shell alias would make it more convenient.  
(Version 1.0)

CHUCK HOUPT  Well, I'll grant you there isn't a large point to this app, but it can be mildly useful. Less itself is a good tool - particularly useful for dealing with huge log files. The Less Termlet just provides convenient access to Less from the Finder environment, and allows some simple customization (window size, font, etc).

Of course, the green-bar paper background is purely for fun. For daily use, I'd recommend reseting the background.  
(Version 1.0)