This is a really cool tool from Microsoft billed as 'a jQuery Interactive Design Tool', basically it allows you to easily create jQuery effects on your site without having to write any JavaScript code!
So what do you get? Well when you start Glimmer up for the first time you are presented with the main Glimmer window displaying four wizard options. These are Image Sequencer, 
Dropdown Menu Wizard, Custom and Tooltip Wizard. Each of these Wizards will step you though creating the designated jQuery effect.
The wizards allow you to easily create what would normally be relatively complex jQuery effect with little effort and if this is your first brush with jQuery it's a very good place to start.
The Tooltip, Dropdown Menu and Image Sequencer wizards are relatively self explanatory, stepping through these wizards will produce html, JavaScript and CSS file necessary to implement the desired effect that you can then use in your own site. However the custom wizard allows you to get a bit more creative as you can create your own jQuery scripts. In custom mode you can open an existing html page and start creating a jQuery script that will operate on the elements in the page.
Along with the cool wizards that come pre-installed Glimmer also offers the ability for extension with custom plug-ins, full details can be found in the help that comes with Glimmer. You have the option of creating custom effects or creating a custom wizard.
I think this is a really cool tool that you must checkout. I've used to produce jQuery effects that I prefer to the equivalent ASP.Net controls. Once word spreads and more custom wizards and effects are produced this will become a truly awesome tool, so go get it and spread the word.