the tiddly wiki system actually really concurs with omnifocus and things in this GTD approach. though things and omnifocus have the better overall design, tiddlywiki - as said - is ultraportable, very lightweighted, and runs in your favorite browser.

its tagging system is superior to the one of things. due to its natural html structure you are possibly easily able to remotely use it from elsewhere.

one additional advantage of the html approach is, that you are able to customize your favorite colours.

as it is available for free you should really give it a try.

Script or App, doesn't much matter It's self-contained & PORTABLE so it has my vote. if You're tired of syncing or worrying about syncing heres a simple solution.

It can be argued that this is an app written in Javascript and packaged as a single HTML file... hopefully admin can speak up about where to draw the line between apps and merely complex scripts.

well, this is not exactly a app but a html page...