I'm releasing a beta build of something I've been working on called jqalert. It's basically a nice, skinnable modal dialog box that defaults to have a certain "fade-in" feel I wanted to have.

Here's the current project URL:

http://www.jondavis.net/codeprojects/jqalert/  

.. or on cachefile:

http://cachefile.net/scripts/jquery/plugins/jqalert/0.9/

I built this having been inspired by a few other similar libraries out there, including:

• lightbox @ http://www.huddletogether.com/projects/lightbox/ 
  • the one that started it all
• blockUI @ http://www.malsup.com/jquery/block/
  • the library most like my own, although inherently different (and better, so far) at literally blocking the UI

What sets jqalert apart is that it is a) specifically an alert() replacement, b) prefab'd to be functionally comparable to Visual Basic's MsgBox, which allows the user to set the title and the icon (and the buttons, too, but jqalert currently only supports OK), while c) also adding a lot of customizeability.

What does "specifically an alert() replacement" really mean, when other tools do the same basic thing? It's about the execution...

• As quick and simple to use as possible: jqalert(message); or jqalert(message, title);
• Predictable "windowing" appearance; universally recognizeable.
• You get a titlebar.
• You can drag the alert window around with the titlebar, for those "emergencies" where you might need to peek back behind the alert window, without closing out the message. 
• You get an OK button.
• The OK button claims focus, so that you can close it by just hitting spacebar or enter.
• The OK button reclaims focus if it loses focus by clicking elsewhere in the alert window.
• Modality blocks UI.